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Subsections

35. Pseudopotential plane-wave density functional theory (NWPW)

The NWChem plane-wave (NWPW) module uses pseudopotentials and plane-wave basis sets to perform Density Functional Theory calculations. This module complements the capabilities of the more traditional Gaussian function based approaches (i.e. DFT module and GAPPS Module) by having an accuracy at least as good as the traditional Gaussian function based approaches for many applications, yet is still fast enough to treat systems containing hundreds of atoms. Another significant advantage is its ability to simulate dynamics on a ground state potential surface directly at run-time using the Car-Parrinello algorithm. This method's efficiency and accuracy make it a desirable first principles method of simulation in the study of complex molecular, liquid, and solid state systems. Applications for this first principles method include the calculation of free energies, search for global minima, explicit simulation of solvated molecules, and simulations of complex vibrational modes that cannot be described within the harmonic approximation.

The NWPW module is a collection of three modules.

The PSPW, Band, and PAW modules can be used to compute the energy and optimize the geometry. Both the PSPW and Band modules can also be used to find saddle points, and compute numerical second derivatives. In addition the PSPW module can also be used to perform Car-Parrinello molecular dynamics.

Section 35.1 describes the tasks contained within the PSPW module, section 35.2 describes the tasks contained within the Band module, section 35.3 describes the tasks contained within the PAW module, and section 35.4 describes the pseudopotential library included with NWChem. The datafiles used by the PSPW module are described in section 35.5. Car-Parrinello output data files are described in section 35.5.8, and the minimization and Car-Parrinello algorithms are described in sections [*]-35.6. Examples of how to setup and run a PSPW geometry optimization, a Car-Parrinello simulation, a band structure minimization, and a PAW geometry optimization are presented in sections 35.7, 35.8, and 35.11, and 35.12. Finally in section 35.13 the capabilities and limitations of the NWPW module are discussed.

If you are a first time user of this module it is recommended that you skip the next five sections and proceed directly to the tutorials in sections 35.7-35.12.


35.1 PSPW Tasks

All input to the PSPW Tasks is contained within the compound PSPW block, 

PSPW
   ...
END

To perform an actual calculation a TASK PSPW directive is used (Section 5.10). 

  TASK PSPW
In addition to the directives listed in Section 5.10, i.e. 
TASK pspw energy          
TASK pspw gradient         
TASK pspw optimize         
TASK pspw saddle           
TASK pspw freqencies       
TASK pspw vib
there are additional directives that are specific to the PSPW module, which are: 
TASK PSPW [Car-Parrinello             ||
           pspw_dplot                 ||
           wannier                    ||
           psp_generator              ||
           steepest_descent           ||
           psp_formatter              ||
           wavefunction_initializer   ||
           v_wavefunction_initializer ||
           wavefunction_expander       ]

Once a user has specified a geometry, the PSPW module can be invoked with no input directives (defaults invoked throughout). However, the user will probably always specify the simulation cell used in the computation, since the default simulation cell is not well suited for most systems. There are sub-directives which allow for customized application; those currently provided as options for the PSPW module are: 

PSPW
  CELL_NAME <string cell_name default 'cell_default'>
  INPUT_WAVEFUNCTION_FILENAME  <string input_wavefunctions  default input_movecs>
  OUTPUT_WAVEFUNCTION_FILENAME <string output_wavefunctions default input_movecs>
  FAKE_MASS <real fake_mass default 400000.0>
  TIME_STEP <real time_step default 5.8>
  LOOP <integer inner_iteration outer_iteration default 10 100>
  TOLERANCES <real tole tolc default 1.0e-7 1.0e-7>
  ENERGY_CUTOFF       <real ecut default (see input description)>
  WAVEFUNCTION_CUTOFF <real wcut default (see input description)>
  EWALD_NCUT <integer ncut default 1>]
  EWALD_RCUT <real rcut default (see input description)>
  XC (Vosko || PBE96  default Vosko)
  DFT||ODFT||RESTRICTED||UNRESTRICTED
  MULT <integer mult default 1>
  MULLIKEN
  ALLOW_TRANSLATION

  SIMULATION_CELL            ... (see input description) END
  DPLOT                      ... (see input description) END
  WANNIER                    ... (see input description) END
  CAR-PARRINELLO             ... (see input description) END
  PSP_GENERATOR              ... (see input description) END
  WAVEFUNCTION_INITIALIZER   ... (see input description) END
  V_WAVEFUNCTION_INITIATIZER ... (see input description) END
  WAVEFUNCTION_EXPANDER      ... (see input description) END
  STEEPEST_DESCENT           ... (see input description) END
END

The following list describes the keywords contained in the PSPW input block.

A prototype limited memory BFGS (LMBFGS) minimizer can be used to minimize the energy. To use this new optimizer the following SET directive needs to be specified: 

set nwpw:mimimizer 1  # Default - Grassman conjugate gradient minimizer is used to minimize the energy.
set nwpw:mimimizer 2  # Grassman LMBFGS minimimzer is used to minimize the energy.
set nwpw:minimizer 4  # Stiefel conjugate gradient minimizer is used to minimize the energy. 
set nwpw:minimizer 5  # Band-by-band minimizer is used to minimize the energy.
Limited testing suggests that the Grassman LMBFGS minimizer is about twice as fast as the conjugate gradient minimizer. However, there are several known cases where this optimizer fails, so it is currently not a default option, and should be used with caution.

In addition the following SET directives can be specified: 

set nwpw:lcao_skip .false. # Default - initial wavefunctions generated using an LCAO guess. 
set nwpw:lcao_skip .true.  # Initial wavefunctions generated using a random plane-wave guess.

set nwpw:lcao_print .false. # Default - Ouput not produced during the generation of the LCAO guess. 
set nwpw:lcao_print .true.  # Output produced during the generation of the LCAO guess.

set nwpw:lcao_iterations 2  #specifies the number of LCAO iterations


35.1.1 Simulation Cell

Simulation cells are stored in the RTDB. To enter a simulation cell into the RTDB the user defines a simulation_cell sub-block within the PSPW block. Listed below is the format of a simulation_cell sub-block. 
PSPW
...
   SIMULATION_CELL
      CELL_NAME <string name default 'cell_default'>
      BOUNDARY_CONDITIONS (periodic || aperiodic default periodic)
      LATTICE_VECTORS
        <real a1.x a1.y a1.z default 20.0  0.0  0.0>
        <real a2.x a2.y a2.z default  0.0 20.0  0.0>
        <real a3.x a3.y a3.z default  0.0  0.0 20.0>
      NGRID <integer na1 na2 na3 default 32 32 32>
   END
...
END
Basically, the user needs to enter the dimensions, gridding and boundry conditions of the simulation cell. The following list describes the input in detail.

35.1.2 (

Unit Cell Optimization

The PSPW module using the DRIVER geometry optimizer can optimize a crystal unit cell. Currently this type of optimization works only if the geometry is specified in fractional coordinates. The following SET directive is used to tell the DRIVER geometry optimizer to optimize the crystal unit cell in addition to the geometry. 

set includestress .true.


35.1.3 DPLOT

The pspw dplot task is used to generate plots of various types of electron densities (or orbitals) of a molecule. The electron density is calculated on the specified set of grid points from a PSPW calculation. The output file generated is in the Gaussian Cube format. Input to the DPLOT task is contained within the DPLOT sub-block. 
PSPW
  ...
  DPLOT
     ...
  END
  ...
END
To run a DPLOT calculation the following directive is used: 
TASK PSPW PSPW_DPLOT
Listed below is the format of a DPLOT sub-block. 
PSPW
... 
   DPLOT
     VECTORS <string input_wavefunctions  default input_movecs>  
     DENSITY [total||difference||alpha||beta||laplacian||potential default total] <string density_name no default>
     ELF [restricted|alpha|beta] <string elf_name no default>
     ORBITAL <integer orbital_number no default> <string orbital_name no default>
   END
...
END
The following list describes the input for the DPLOT sub-block.


35.1.4 Wannier

The pspw wannier task is generate maximally localized (Wannier) molecular orbitals. The algorithm proposed by Silvestrelli et al is use to generate the Wannier orbitals. The current version of this code works only for cubic cells.

Input to the Wannier task is contained within the Wannier sub-block. 

PSPW
  ...
  Wannier
     ...
  END
  ...
END
To run a Wannier calculation the following directive is used: 
TASK PSPW Wannier
Listed below is the format of a Wannier sub-block. 
PSPW
... 
   Wannier
     OLD_WAVEFUNCTION_FILENAME <string input_wavefunctions  default input_movecs>  
     NEW_WAVEFUNCTION_FILENAME <string output_wavefunctions default input_movecs>
   END
...
END
The following list describes the input for the Wannier sub-block.


35.1.5 Self-Interaction Corrections

The SET directive is used to specify the molecular orbitals contribute to the self-interaction-correction (SIC) term. 

set pspw:SIC_orbitals  <integer list_of_molecular_orbital_numbers>
This defines only the molecular orbitals in the list as SIC active. All other molecular orbitals will not contribute to the SIC term.

For example the following directive specifies that the molecular orbitals numbered 1,5,6,7,8, and 15 are SIC active. 

set pspw:SIC_orbitals  1 5:8 15
or equivalently 
set pspw:SIC_orbitals  1 5 6 7 8 15

The following directive turns on self-consistent SIC. 

set pspw:SIC_relax 	.false.  # Default - Perturbative SIC calculation
set pspw:SIC_relax 	.true.   # Self-consistent SIC calculation

Two types of solvers can be used and they are specified using the following SET directive 

set pspw:SIC_solver_type 1  # Default - cutoff coulomb kernel
set pspw:SIC_solver_type 2  # Free-space boundary condition kernel
The parameters for the cutoff coulomb kernel are defined by the following SET directives: 
set pspw:SIC_screening_radius <real rcut>
set pspw:SIC_screening_power  <real rpower>


35.1.6 Point Charge Analysis

The MULLIKEN option can be used to generate derived atomic point charges from a plane-wave density. This analysis is based on a strategy suggested in the work of P.E. Blochl, J. Chem. Phys. vol. 103, page 7422 (1995). In this strategy the low-frequency components a plane-wave density are fit to a linear combination of atom centered Gaussian functions.

The following SET directives are used to define the fitting. 

set pspw_APC:Gc <real Gc_cutoff>  # specifies the maximum frequency component of the density to be used in the fitting in units of au.

set pspw_APC:nga <integer number_gauss> # specifies the the number of Gaussian functions per
atom.

set pspw_APC:gamma <real gamma_list> # specifies the decay lengths of each atom centered Gaussian.

We suggest using the following parameters. 

set pspw_APC:Gc 2.5
set pspw_APC:nga 3
set pspw_APC:gamma 0.6 0.9 1.35


35.1.7 Car-Parrinello

The Car-Parrinello task is used to perform ab initio molecular dynamics using the scheme developed by Car and Parrinello. In this unified ab initio molecular dynamics scheme the motion of the ion cores is coupled to a fictitious motion for the Kohn-Sham orbitals of density functional theory. Constant energy or constant temperature simulations can be performed. A detailed description of this method is described in section 35.6.

Input to the Car-Parrinello simulation is contained within the Car-Parrinello sub-block. 

PSPW
  ...
  Car-Parrinello
     ...
  END
  ...
END
To run a Car-Parrinello calculation the following directive is used: 
TASK PSPW Car-Parrinello
The Car-Parrinello sub-block contains a great deal of input, including pointers to data, as well as parameter input. Listed below is the format of a Car-Parrinello sub-block. 
PSPW
...
   Car-Parrinello
      CELL_NAME <string cell_name default 'cell_default'>
      INPUT_WAVEFUNCTION_FILENAME    <string input_wavefunctions    default input_movecs>
      OUTPUT_WAVEFUNCTION_FILENAME   <string output_wavefunctions   default input_movecs>
      INPUT_V_WAVEFUNCTION_FILENAME  <string input_v_wavefunctions  default input_vmovecs>
      OUTPUT_V_WAVEFUNCTION_FILENAME <string output_v_wavefunctions default input_vmovecs>
      FAKE_MASS <real fake_mass default default 1000.0>
      TIME_STEP <real time_step default 5.0>
      LOOP <integer inner_iteration outer_iteration default 10 1>
      SCALING <real scale_c scale_r default 1.0 1.0>
      ENERGY_CUTOFF       <real ecut default (see input description)>
      WAVEFUNCTION_CUTOFF <real wcut default (see input description)>
      EWALD_NCUT <integer ncut default 1>
      EWALD_RCUT <real rcut    default (see input description)>
      XC (Vosko || PBE96  default Vosko)
      [Nose-Hoover <real Period_electron Temperature_electrion Period_ion Temperature_ion 
                          default 100.0 298.15 100.0 298.15>]
      [SA_decay <real sa_scale_c sa_scale_r default 1.0 1.0>]
      XYZ_FILENAME <string xyz_filename default XYZ>
      EMOTION_FILENAME <string emotion_filename default EMOTION>
      HMOTION_FILENAME <string hmotion_filename default HMOTION>
      OMOTION_FILENAME <string omotion_filename default OMOTION>
      EIGMOTION_FILENAME <string eigmotion_filename default EIGMOTION>
      ION_MOTION_FILENAME <string ion_motion_filename default MOTION>

   END
...

END
The following list describes the input for the Car-Parrinello sub-block.

When a DPLOT sub-block is specified the following SET directive can be used to output dplot data during a Car-Parrinello simulation: 

set pspw_dplot:iteration_list <integer list_of_iteration_numbers>
The Gaussian cube files specified in the DPLOT sub-block are appended with the specified iteration number.

For example, the following directive specifies that at the 3,10,11,12,13,14,15, and 50 iterations Gaussian cube files are to be produced. 

set pspw_dplot:iteration_list 3,10:15,50


35.1.8 PSP_GENERATOR

A one-dimensional pseudopotential code has been integrated into NWChem. This code allows the user to modify and develop pseudopotentials. Currently, only the Hamann and Troullier-Martins norm-conserving pseudopotentials can be generated. In future releases, the pseudopotential library (section 35.4) will be more complete, so that the user will not have explicitly generate pseudopotentials using this module.

Input to the PSP_GENERATOR task is contained within the PSP_GENERATOR sub-block. 

PSPW
  ...
  PSP_GENERATOR
     ...
  END
  ...
END
To run a PSP_GENERATOR calculation the following directive is used: 
TASK PSPW PSP_GENERATOR
Listed below is the format of a PSP_GENERATOR sub-block. 
PSPW
... 
   PSP_GENERATOR
      PSEUDOPOTENTIAL_FILENAME: <string psp_name>
      ELEMENT: <string element>
      CHARGE: <real charge>
      MASS_NUMBER: <real mass_number>
      ATOMIC_FILLING: <integer ncore nvalence>
      ( (1||2||...) (s||p||d||f||...) <real filling> \
         ...)
      
      [CUTOFF: <integer lmax> 
         ( (s||p||d||f||g) <real rcut>\
         ...)
      ]
      PSEUDOPOTENTIAL_TYPE: (TROULLIER-MARTINS || HAMANN default HAMANN)
      SOLVER_TYPE: (PAULI || SCRHODINGER default PAULI)
      EXCHANGE_TYPE: (dirac || PBE96 default DIRAC)
      CORRELATION_TYPE: (VOSKO || PBE96 default VOSKO)
      [SEMICORE_RADIUS: <real rcore>]
      
   end
... 
END
The following list describes the input for the PSP_GENERATOR sub-block.

35.1.8.1 ATOMIC_FILLING Block

This required block is used to define the reference atom which is used to define the pseudopotential. After the ATOMIC_FILLING: $<$ncore$>$ $<$nvalence$>$ line, the core states are listed (one per line), and then the valence states are listed (one per line). Each state contains two integer and a value. The first integer specifies the radial quantum number, $n$, The second integer specifies the angular momentum quantum number, $l$, and the third value specifies the occupation of the state.

For example to define a pseudopotential for the Neon atom in the $1s^2 2s^2 2p^6$ state could have the block 

ATOMIC_FILLING: 1 2
        1  s  2.0   #core state    - 1s^2 
        2  s  2.0   #valence state - 2s^2
        2  p  6.0   #valence state - 2p^6
for a pseudopotential with a $2s$ and $2p$ valence electrons or the block 
ATOMIC_FILLING: 3 0
        1  s  2.0    #core state
        2  s  2.0    #core state
        2  p  6.0    #core state
could be used for a pseudopotential with no valence electrons.

35.1.8.2 CUTOFF Block

This optional block specifies the cutoff distances used to match the all-electron atom to the pseudopotential atom. For Hamann pseudopotentials $r_{cut}(l)$ defines the distance where the all-electron potential is matched to the pseudopotential, and for Troullier-Martins pseudopotentials $r_{cut}(l)$ defines the distance where the all-electron orbital is matched to the pseudowavefunctions. Thus the definition of the radii depends on the type of pseudopotential. The cutoff radii used in Hamann pseudopotentials will be smaller than the cufoff raddi used in Troullier-Martins pseudopotentials.

For example to define a softened Hamann pseudopotential for Carbon would be 

ATOMIC_FILLING: 1 2
  1  s  2.0
  2  s  2.0
  2  p  2.0
CUTOFF: 2
  s  0.8
  p  0.85
  d  0.85
while a similarly softened Troullier-Marting pseudopotential for Carbon would be 
ATOMIC_FILLING: 1 2
  1  s  2.0
  2  s  2.0
  2  p  2.0
CUTOFF: 2
  s  1.200
  p  1.275
  d  1.275

35.1.8.3 SEMICORE_RADIUS Option

Specifying the SEMICORE_RADIUS option turns on the semicore correction approximation proposed by Louie et al (S.G. Louie, S. Froyen, and M.L. Cohen, Phys. Rev. B, 26, 1738, (1982)). This approximation is known to dramatically improve results for systems containing alkali and transition metal atoms.

The implmentation in the PSPW module defines the semi-core denisty, $\rho_{semicore}$ in terms of the core density, $\rho_{core}$, by using the sixth-order polynomial

$\displaystyle \rho_{semicore}(r) = \left\{ \begin{array}{ll} \rho_{core} & \mbo... ...+ c_4 r^4 + c_5 r^5 + c_6 r^6 & \mbox{if $r < r_{semicore}$} \end{array}\right.$     (35.1)

This expansion was suggested by Fuchs and Scheffler (M. Fuchs, and M. Scheffler, Comp. Phys. Comm.,119,67 (1999)), and is better behaved for taking derivatives (i.e. calculating ionic forces) than the expansion suggested by Louie et al.


35.1.9 WAVEFUNCTION_INTITIALIZER

The functionality of this task is now performed automatically. For backwards compatibility, we provide a description of the input to this task.

The wavefunction_initializer task is used to generate an initial wavefunction datafile. Input to the WAVEFUNCTION_INITIALIZER task is contained within the WAVEFUNCTION_INITIALIZER sub-block. 

PSPW
  ...
  WAVEFUNCTION_INITIALIZER
     ...
  END
  ...
END
To run a WAVEFUNCTION_INITIALIZER calculation the following directive is used: 
TASK PSPW WAVEFUNCTION_INITIALIZER
Listed below is the format of a WAVEFUNCTION_INITIALIZER sub-block. 
PSPW
... 
   WAVEFUNCTION_INITIALIZER
     CELL_NAME: <string cell_name>
     WAVEFUNCTION_FILENAME: <string wavefunction_name default input_movecs>
     (RESTRICTED||UNRESTRICTED)
     if (RESTRICTED)   
        RESTRICTED_ELECTRONS: <integer restricted electrons>
     if (UNRESTRICTED) 
        UP_ELECTRONS: <integer up_electrons>
        DOWN_ELECTRONS: <integer down_electrons>
   END
...
END
The following list describes the input for the WAVEFUNCTION_INITIALIZER sub-block.

35.1.9.1 Old Style Input (version 3.3) to WAVEFUNCTION_INTITIALIZER

For backwards compatibility, the input to the WAVEFUNCTION_INITIALIZER sub-block can also be of the form 

PSPW
... 
   WAVEFUNCTION_INITIALIZER
     CELL_NAME: <string cell_name>
     WAVEFUNCTION_FILENAME: <string wavefunction_name default input_movecs>
     (RESTRICTED||UNRESTRICTED)
     
     [UP_FILLING: <integer up_filling>
        [0 0 0   0]
        {<integer kx ky kz> (-2||-1||1||2)}]
     [DOWN_FILLING: <integer down_filling>
        [0 0 0   0]
        {<integer kx ky kz> (-2||-1||1||2)}]
   END
...
END
where

The values for the planewave $(-2\vert\vert-1\vert\vert 1\vert\vert 2)$ are used to represent whether the specified planewave is a cosine or a sine function, in addition random noise can be added to these base functions. That is $+1$ represents a cosine function, and $-1$ represents a sine function. The $+2$ and $-2$ values are used to represent a cosine function with random components added and a sine function with random components added respectively.


35.1.10 V_WAVEFUNCTION_INITIALIZER

The functionality of this task is now performed automatically. For backwards compatibility, we provide a description of the input to this task.

The v_wavefunction_initializer task is used to generate an initial velocity wavefunction datafile. Input to the V_WAVEFUNCTION_INITIALIZER task is contained within the V_WAVEFUNCTION_INITIALIZER sub-block. 

PSPW
  ...
  V_WAVEFUNCTION_INITIALIZER
     ...
  END
  ...
END
To run a V_WAVEFUNCTION_INITIALIZER calculation the following directive is used: 
TASK PSPW WAVEFUNCTION_INITIALIZER
Listed below is the format of a V_WAVEFUNCTION_INITIALIZER sub-block. 
PSPW
... 
   V_WAVEFUNCTION_INITIALIZER
     V_WAVEFUNCTION_FILENAME: <string v_wavefunction_name default input_vmovecs>
     CELL_NAME: <string cell_name>
     (RESTRICTED||UNRESTRICTED)
     UP_FILLING: <integer up_filling>
     DOWN_FILLING: <integer down_filling>
   END
...
END
The following list describes the input for the V_WAVEFUNCTION_INITIALIZER sub-block.


35.1.11 WAVEFUNCTION_EXPANDER

The wavefunction_expander task is used to convert a new wavefunction file that spans a larger grid space from an old wavefunction file. Input to the WAVEFUNCTION_EXPANDER task is contained within the WAVEFUNCTION_EXPANDER sub-block. 
PSPW
  ...
  WAVEFUNCTION_EXPANDER
     ...
  END
  ...
END
To run a WAVEFUNCTION_EXPANDER calculation the following directive is used: 
TASK PSPW WAVEFUNCTION_EXPANDER
Listed below is the format of a WAVEFUNCTION_EXPANDER sub-block. 
PSPW
... 
   WAVEFUNCTION_EXPANDER   
     OLD_WAVEFUNCTION_FILENAME: <string old_wavefunction_name default input_movecs>
     NEW_WAVEFUNCTION_FILENAME: <string new_wavefunction_name default input_movecs>
     NEW_NGRID: <integer na1 na2 na3>
    
   END
...
END
The following list describes the input for the WAVEFUNCTION_EXPANDER sub-block.


35.1.12 STEEPEST_DESCENT

The functionality of this task is now performed automatically by the PSPW minimizer. For backwards compatibility, we provide a description of the input to this task.

The steepest_descent task is used to optimize the one-electron orbitals with respect to the total energy. In addition it can also be used to optimize geometries. This method is meant to be used for coarse optimization of the one-electron orbitals. A detailed description of the this method is described in section [*]

Input to the steepest_descent simulation is contained within the steepest_descent sub-block. 

PSPW
  ...
  STEEPEST_DESCENT
     ...
  END
  ...
END
To run a steepest_descent calculation the following directive is used: 
TASK PSPW steepest_descent
The steepest_descent sub-block contains a great deal of input, including pointers to data, as well as parameter input. Listed below is the format of a STEEPEST_DESCENT sub-block. 
PSPW
...
   STEEPEST_DESCENT
      CELL_NAME <string cell_name>
      [GEOMETRY_OPTIMIZE]
      INPUT_WAVEFUNCTION_FILENAME  <string input_wavefunctions  default input_movecs>
      OUTPUT_WAVEFUNCTION_FILENAME <string output_wavefunctions default input_movecs>
      FAKE_MASS <real fake_mass default 400000.0>
      TIME_STEP <real time_step default 5.8>
      LOOP <integer inner_iteration outer_iteration default 10 1>
      TOLERANCES <real tole tolc tolr default 1.0d-9 1.0d-9 1.0d-4>
      ENERGY_CUTOFF       <real ecut default (see input desciption)>
      WAVEFUNCTION_CUTOFF <real wcut default (see input description)>
      EWALD_NCUT <integer ncut default 1>
      EWALD_RCUT <real rcut default (see input description)>
      XC (Vosko || PBE96  default Vosko)
      [MULLIKEN]

   END
...

END
The following list describes the input for the STEEPEST_DESCENT sub-block.


35.2 Band Tasks

All input to the Band Tasks is contained within the compound NWPW block, 

NWPW
   ...
END

To perform an actual calculation a TASK Band directive is used (Section 5.10). 

  TASK Band

Once a user has specified a geometry, the Band module can be invoked with no input directives (defaults invoked throughout). There are sub-directives which allow for customized application; those currently provided as options for the Band module are: 

NWPW
  CELL_NAME <string cell_name default 'cell_default'>
  ZONE_NAME <string zone_name default 'zone_default'>
  INPUT_WAVEFUNCTION_FILENAME  <string input_wavefunctions  default input_movecs>
  OUTPUT_WAVEFUNCTION_FILENAME <string output_wavefunctions default input_movecs>
  FAKE_MASS <real fake_mass default 400000.0>
  TIME_STEP <real time_step default 5.8>
  LOOP <integer inner_iteration outer_iteration default 10 100>
  TOLERANCES <real tole tolc default 1.0e-7 1.0e-7>
  ENERGY_CUTOFF       <real ecut default (see input description)>
  WAVEFUNCTION_CUTOFF <real wcut default (see input description)>
  EWALD_NCUT <integer ncut default 1>]
  EWALD_RCUT <real rcut default (see input description)>
  EXCHANGE_CORRELATION: (Vosko || PBE96  default Vosko)
  DFT||ODFT||RESTRICTED||UNRESTRICTED
  MULT <integer mult default 1>
  
  SIMULATION_CELL ... (see input description) END
  BRILLOUIN_ZONE  ... (see input description) END

END
The following list describes these keywords.


35.2.1 Brillouin Zone

The special points of the Brillouin zone for a Band structure calculation are stored in the RTDB. To enter special points of the Brillouin zone into the RTDB the user defines a brillouin_zone sub-block within the NWPW block. Listed below is the format of a brillouin_zone sub-block. 
NWPW
...
   BRILLOUIN_ZONE
      ZONE_NAME <string name default 'zone_default'>
      (KVECTOR <real k1 k2 k3 no default> <real weight default (see input description)>
       ...)
   END
...
END
The user enters the special points and weights of the Brillouin zone. The following list describes the input in detail.


35.3 PAW Tasks

All input to the PAW Tasks is contained within the compound NWPW block, 

NWPW
   ...
END

To perform an actual calculation the following is used (Section 5.10). 

  TASK PAW steepest\_descent

Once a user has specified a geometry, the PAW module can be invoked with no input directives (defaults invoked throughout). There are sub-directives which allow for customized application; those currently provided as options for the PAW module are: 

NWPW
  CELL_NAME <string cell_name default 'cell_default'>  
  [GEOMETRY_OPTIMIZE]
  INPUT_WAVEFUNCTION_FILENAME  <string input_wavefunctions  default input_movecs>
  OUTPUT_WAVEFUNCTION_FILENAME <string output_wavefunctions default input_movecs>
  FAKE_MASS <real fake_mass default 400000.0>
  TIME_STEP <real time_step default 5.8>
  LOOP <integer inner_iteration outer_iteration default 10 100>
  TOLERANCES <real tole tolc default 1.0e-7 1.0e-7>
  ENERGY_CUTOFF       <real ecut default (see input description)>
  WAVEFUNCTION_CUTOFF <real wcut default (see input description)>
  EWALD_NCUT <integer ncut default 1>]
  EWALD_RCUT <real rcut default (see input description)>
  EXCHANGE_CORRELATION: (Vosko || PBE96  default Vosko)
  DFT||ODFT||RESTRICTED||UNRESTRICTED
  MULT <integer mult default 1>
  
  SIMULATION_CELL ... (see input description) END

END
The following list describes these keywords.


35.4 Pseudopotential and PAW basis Libraries

A library of pseudopotentials used by PSPW and BAND is currently available in the directory
$NWCHEM_TOP/src/nwpw/libraryps/library1

The elements listed in the following table are present: 

  H
 -------
  Li Be                               B  C  N  O
 -------                             ------------------
                                      Al Si P  S     
 ------------------------------------------------------
                                   Zn Ga               
 ------------------------------------------------------

Similary, a library of PAW basis used by PAW is currently available in the directory
$NWCHEM_TOP/src/nwpw/libraryps/library2

Currently there are not very many elements available for PAW. However, the user can request additional basis sets from Eric J. Bylaska at (nwchem-support@emsl.pnl.gov or eric.bylaska@pnl.gov) The elements available are: H, O Al, Sc, V, and Fe.

If you wish to redirect the code to a different directory other than the default one, you need to set the environmental variable NWCHEM_NWPW_LIBRARY to the new location of the libraryps directory.


35.5 NWPW RTDB Entries and DataFiles

Input to the PSPW and Band modules are contained in both the RTDB and datafiles. The RTDB is used to store input that the user will need to directly specify. Input of this kind includes ion positions, ion velocities, and simulation cell parameters. The datafiles are used to store input, such the one-electron orbitals, one-electron orbital velocities, formatted pseudopotentials, and one-dimensional pseudopotentials, that the user will in most cases run a program to generate.

35.5.1 Ion Positions

The positions of the ions are stored in the default geometry structure in the RTDB and must be specified using the GEOMETRY directive.

35.5.2 Ion Velocities

The velocities of the ions are stored in the default geometry structure in the RTDB, and must be specified using the GEOMETRY directive.


35.5.3 ANALYSIS: Mulliken RTDB data

To perform Mulliken analysis information is needed from one-dimensional pseudopotential files. In-order to facilitate the transfer of this information to the simulation the ANALYSIS sub-block is used to exract the necessary information and put it into the RTDB. 

PSPW
...
   ANALYSIS
      (psp_filename: <string psp_name> \
       ...)
   END
...
END
Basically, the user needs to enter each pseudopotential used in the simulation.

35.5.4 Wavefunction Datafile

The one-electron orbitals are stored in a wavefunction datafile. This is a binary file and cannot be directly edited. This datafile is used by steepest_descent and Car-Parrinello tasks and can be generated using the wavefunction_initializer or wavefunction_expander tasks.

35.5.5 Velocity Wavefunction Datafile

The one-electron orbital velocities are stored in a velocity wavefunction datafile. This is a binary file and cannot be directly edited. This datafile is used by the Car-Parrinello task and can be generated using the v_wavefunction_initializer task.

35.5.6 Formatted Pseudopotential Datafile

The pseudopotentials in Kleinman-Bylander form expanded on a simulation cell (3d grid) are stored in a formatted pseudopotential datafile. This is a binary file and cannot be directly edited. This datafile is used by steepest_descent and Car-Parrinello tasks and can be generated using the pseudpotential_formatter task.

35.5.7 One-Dimensional Pseudopotential Datafile

The one-dimensional pseudopotentials are stored in a one-dimensional pseudopotential file. This is an ascii file and can be directly edited with a text editor. However, the user will usually use the psp_generator task to generate this datafile.

The data stored in the one-dimensional pseudopotential file is 

   character*2 element       :: element name
   integer     charge        :: valence charge of ion
   real        mass          :: mass of ion
   integer     lmax          :: maximum angular component
   real        rcut(lmax)    :: cutoff radii used to define pseudopotentials
   integer     nr            :: number of points in the radial grid
   real        dr            :: linear spacing of the radial grid
   real        r(nr)         :: one-dimensional radial grid
   real        Vpsp(nr,lmax) :: one-dimensional pseudopotentials
   real        psi(nr,lmax)  :: one-dimensional pseudowavefunctions
   real        r_semicore        :: semicore radius
   real        rho_semicore(nr)  :: semicore density
and the format of it is: 
[line 1:     ] element  
[line 2:     ] charge mass lmax
[line 3:     ] (rcut(l), l=1,lmax)
[line 4:     ] nr dr
[line 5:     ]    r(1)  (Vpsp(1,l),  l=1,lmax)
[line 6:     ] ....
[line nr+4:  ] r(nr) (Vpsp(nr,l), l=1,lmax)
[line nr+5:  ] r(1)  (psi(1,l), l=1,lmax) 
[line nr+6:  ] ....
[line 2*nr+4:] r(nr) (psi(nr,l), l=1,lmax)
[line 2*nr+5:] r_semicore
if (r_semicore read) then
[line 2*nr+6:] r(1)  rho_semicore(1)
[line 2*nr+7:] ....
[line 3*nr+5:] r(nr) rho_semicore(nr)
end if


35.5.8 PSPW Car-Parrinello Output Datafiles

35.5.8.1 XYZ motion file

Data file that stores ion positions and velocities as a function of time in XYZ format. 

[line 1:          ]  n_ion
[line 2:          ]  
do ii=1,n_ion
[line 2+ii:       ] atom_name(ii), x(ii),y(ii),z(ii),vx(ii),vy(ii),vz(ii)
end do
[line n_ion+3     ] n_nion

do ii=1,n_ion
[line n_ion+3+ii: ] atom_name(ii), x(ii),y(ii),z(ii), vx(ii),vy(ii),vz(ii)
end do
[line 2*n_ion+4:  ]  ....

35.5.8.2 ION_MOTION motion file

Datafile that stores ion positions and velocities as a function of time 

[line 1:          ]  it_out, n_ion, omega
[line 2:          ]  time
do ii=1,n_ion
[line 2+ii:       ] x(ii),y(ii),z(ii), vx(ii),vy(ii),vz(ii)
end do
[line n_ion+3     ] time
do 
do ii=1,n_ion
[line n_ion+3+ii: ] x(ii),y(ii),z(ii), vx(ii),vy(ii),vz(ii)
end do
[line 2*n_ion+4:  ]  ....

35.5.8.3 EMOTION motion file

Datafile that store energies as a function of time 
[line 1:          ]  time, E1,E2,E3,E4,E5,E6,E7,E8, (E9,E10, if Nose-Hoover)
[line 2:          ] ...

35.5.8.4 HMOTION motion file

Datafile that stores the rotation matrix as a function of time. 

[line 1:          ] time
[line 2:          ] ms,ne(ms),ne(ms)
do i=1,ne(ms)
[line 2+i:        ] (hml(i,j), j=1,ne(ms)
end do
[line 3+ne(ms):   ] time
[line 4+ne(ms):   ] ....

35.5.8.5 EIGMOTION motion file

Datafile that stores the eigenvalues for the one-electron orbitals as a function of time. 

[line 1:          ]  time, (eig(i), i=1,number_orbitals)
[line 2:          ] ...

35.5.8.6 OMOTION motion file

Datafile that stores a reduced representation of the one-electron orbitals. To be used with a molecular orbital viewer that will be ported to NWChem in the near future.


35.6 Car-Parrinello Scheme for Ab Initio Molecular Dynamics

Car and Parrinello developed a unified scheme for doing ab initio molecular dynamics by combining the motion of the ion cores and a ficticious motion for the Kohn-Sham orbitals of density-functional theory (R. Car and M. Parrinello, Phys. Rev. Lett. 55, 2471, (1985)). At the heart of this method they introduced a ficticious kinetic energy functional for the Kohn-Sham orbitals.


$\displaystyle KE(\{\psi_{i,\sigma}(\vec{r})\})$ $\textstyle =$ $\displaystyle \sum_{i,\sigma}^{occ} \int d\vec{r}\ \mu \left\vert \dot{\psi}_{i,\sigma}(\vec{r}) \right\vert^2$ (35.2)

Given this kinetic energy the constrained equations of motion are found by taking the first variation of the auxiliary Lagrangian.

$\displaystyle L$ $\textstyle =$ $\displaystyle \sum_{i,\sigma}^{occ} \int d\vec{r}\ \mu \left\vert \dot{\psi}_{i... ...eft[ \left\{ \psi_{i,\sigma}(\vec{r})\right\},\left\{\vec{R}_I \right\} \right]$  
    $\displaystyle +\sum_{ij,\sigma} \Lambda_{ij,\sigma} \left( \int d\vec{r}\ \psi_{i,\sigma}^{*}(\vec{r}) \psi_{j,\sigma}(\vec{r}) - \delta_{ij,\sigma} \right)$ (35.3)

Which generates a dynamics for the wavefunctions $\psi_{i,\sigma}(\vec{r})$ and atoms positions $\vec{R}_I$ through the constrained equations of motion:


$\displaystyle \mu \ddot{\psi}_{i,\sigma}(\vec{r},t)$ $\textstyle =$ $\displaystyle -\frac{\delta E}{\delta \psi_{i,\sigma }^{*} \left( \vec{r},t \ri... ... } + \sum\limits_j \Lambda_{ij,\sigma} \psi_{j,\sigma} \left( \vec{r},t \right)$ (35.4)


$\displaystyle M_I \ddot{\vec{R}}_I$ $\textstyle =$ $\displaystyle -\frac{\partial E}{\partial \vec{R}_I}$ (35.5)

where $\mu$ is the fictitious mass for the electronic degrees of freedom and $M_I$ are the ionic masses. The adjustable parameter $\mu$ is used to describe the relative rate at which the wavefunctions change with time. $\Lambda_{ij,\sigma}$ are the Lagrangian multipliers for the orthonormalization of the single-particle orbitals $\psi_{i,\sigma}(\vec{r})$. They are defined by the orthonormalization constraint conditions and can be rigorously found. However, the equations of motion for the Lagrange multipliers depend on the specific algorithm used to integrate Eqs. 35.4-35.5.

For this method to give ionic motions that are physically meaningful the kinetic energy of the Kohn-Sham orbitals must be relatively small when compared to the kinetic energy of the ions. There are two ways where this criterion can fail. First, the numerical integrations for the Car-Parrinello equations of motion can often lead to large relative values of the kinetic energy of the Kohn-Sham orbitals relative to the kinetic energy of the ions. This kind of failure is easily fixed by requiring a more accurate numerical integration, i.e. use a smaller time step for the numerical integration. Second, during the motion of the system a the ions can be in locations where there is an Kohn-Sham orbital level crossing, i.e. the density-functional energy can have two states that are nearly degenerate. This kind of failure often occurs in the study of chemical reactions. This kind of failure is not easily fixed and requires the use of a more sophisticated density-functional energy that accounts for low-lying excited electronic states.

35.6.1 Verlet Algorithm for Integration

Eqs. 35.4-35.5 integrated using the Verlet algorithm results in


$\displaystyle \psi_{i,\sigma}^{t+ \Delta t}$ $\textstyle \leftarrow$ $\displaystyle 2 \psi_{i,\sigma}^{t} - \psi_{i,\sigma}^{t-\Delta t} + \frac{(\De... ...\psi_{i,\sigma}^{*}} + \sum_{j} \psi_{j,\sigma} \Lambda_{ji,\sigma} \right]_{t}$ (35.6)


$\displaystyle \vec{R}_I^{t+\Delta t}$ $\textstyle \leftarrow$ $\displaystyle 2 \vec{R}_I^{t} - \vec{R}_I^{t-\Delta t} + \frac{(\Delta t)^2}{M_I} \frac{\partial E}{\partial \vec{R}_I}$ (35.7)

In this molecular dynamic procedure we have to know variational derivative $\frac{\delta E}{\delta \psi_{i,\sigma}^{*}}$ and the matrix $\Lambda_{ij,\sigma}$. The variational derivative $\frac{\delta E}{\delta \psi_{i,\sigma}^{*}}$ can be analytically found and is

$\displaystyle \frac{\delta E}{\delta \psi_{i,\sigma}^{*}}$ $\textstyle =$ $\displaystyle -\frac{1}{2} \nabla^2 \psi_{i,\sigma}(\vec{r})$  
  $\textstyle +$ $\displaystyle \int d\vec{r^{\prime}} W_{ext}(\vec{r},\vec{r^{\prime}}) \psi_{i,\sigma}(\vec{r^{\prime}})$  
  $\textstyle +$ $\displaystyle \int d\vec{r^{\prime}} \frac{n(\vec{r^{\prime}})}{\vert\vec{r}-\vec{r^{\prime}}\vert} \psi_{i,\sigma}(\vec{r})$  
  $\textstyle +$ $\displaystyle \mu_{xc}^{\sigma}(\vec{r}) \psi_{i,\sigma}(\vec{r})$  
  $\textstyle \equiv$ $\displaystyle \hat{H} \psi_{i,\sigma}$ (35.8)

To find the matrix $\Lambda_{ij,\sigma}$ we impose the orthonormality constraint on $\psi_{i,\sigma}^{t+\Delta t}$ to obtain a matrix Riccatti equation, and then Riccatti equation is solved by an iterative solution (see section [*]).


35.6.2 Constant Temperature Simulations: Nose-Hoover Thermostats

Nose-Hoover Thermostats for the electrons and ions can also be added to the Car-Parrinello simulation. In this type of simulation thermostats variables $x_e$ and $x_R$ are added to the simulation by adding the auxillary energy functionals to the total energy.

$\displaystyle ION\_THERMOSTAT(x_R)$ $\textstyle =$ $\displaystyle \frac{1}{2} Q_R \dot{x_R} + E_{R0}x_R$ (35.9)
$\displaystyle ELECTRON\_THERMOSTAT(x_e)$ $\textstyle =$ $\displaystyle \frac{1}{2} Q_e \dot{x_e} + E_{e0}x_e$ (35.10)

In these equations, the average kinetic energy for the ions is

$\displaystyle E_{R0} = \frac{1}{2} f k_B T$     (35.11)

where $f$ is the number of atomic degrees of freedom, $k_B$ is Boltzmans constant, and T is the desired temperature. Defining the average ficticious kinetic energy of the electrons is not as straighforward. Blöchl and Parrinello (P.E. Blöchl and M. Parrinello, Phys. Rev. B, 45, 9413, (1992)) have suggested the following formula for determining the average ficticious kinetic energy
$\displaystyle E_{e0} = 4 k_B T \frac{\mu}{M} \sum_i <\psi_i\vert-\frac{1}{2} \nabla^2 \vert\psi_i>$     (35.12)

where $\mu$ is the ficticious electronic mass, $M$ is average mass of one atom, and $\sum_i <\psi_i\vert-\frac{1}{2} \nabla^2 \vert\psi_i>$ is the kinetic energy of the electrons.

Blöchl and Parrinello suggested that the choice of mass parameters, $Q_e$, and $Q_R$ should be made such that the period of oscillating thermostats should be chosen larger than the typical time scale for the dynamical events of interest but shorter than the simulation time.

$\displaystyle P_{ion}$ $\textstyle =$ $\displaystyle 2\pi \sqrt{\frac{Q_R}{4E_{R0}}}$ (35.13)
$\displaystyle P_{electron}$ $\textstyle =$ $\displaystyle 2\pi \sqrt{\frac{Q_e}{4E_{e0}}}$ (35.14)

where $P_{ion}$ and $P_{electron}$ are the periods of oscillation for the ionic and ficatious electronic thermostats.

In simulated annealing simulations the electronic and ionic Temperatures are scaled according to an exponential cooling schedule,

$\displaystyle T_e(t) = T_e^0 \exp^{-\frac{t}{\tau_e}}$     (35.15)
$\displaystyle T_{ionic}(t) = T_{ionic}^0 \exp^{-\frac{t}{\tau_{ionic}}}$     (35.16)

where $T_e^0$ and $T_{ionic}^0$ are the intial temperatures, and $\tau_e$ and $\tau_{ionic}$ are the cooling rates in atomic units.


35.7 PSPW Tutorial 1: Minimizing the geometry for a C$_2$ molecule

In this section we show how use the PSPW module to optimize the geometry for a C$_2$ molecule at the PBE96 levels.

In the following example we show the input needed to optimize the geometry for a C$_2$ molecule at the LDA level. In this example, default pseudopotentials from the pseudopotential library are used for C, the boundary condition is free-space, the exchange correlation functional is PBE96, The boundary condition is free-space, and the simulation cell cell is aperiodic and cubic with a side length of 10.0 Angstroms and has 40 grid points in each direction (cutoff energy is 44 Ry). 

         
start c2_pspw_pbe96
title "C2 restricted singlet dimer optimization - PBE96/44Ry"

geometry  
C    -0.62 0.0 0.0
C     0.62 0.0 0.0
end
       
pspw
   simulation_cell units angstroms
      boundary_conditions aperiodic
      SC 10.0
      ngrid 40 40 40
   end
   xc pbe96
end
set nwpw:minimizer 2
task pspw optimize


35.8 PSPW Tutorial 2: Running a Car-Parrinello Simulation

In this section we show how use the PSPW module to perform a Car-Parrinello molecular dynamic simulation for a C$_2$ molecule at the LDA level. Before running a PSPW Car-Parrinello simulation the system should be on the Born-Oppenheimer surface, i.e. the one-electron orbitals should be minimized with respect to the total energy (i.e. task pspw energy). The input needed is basically the same as for optimizing the geometry of a C$_2$ molecule at the LDA level, except that and additional Car-Parrinello sub-block is added.

In the following example we show the input needed to run a Car-Parrinello simulation for a C$_2$ molecule at the LDA level. In this example, default pseudopotentials from the pseudopotential library are used for C, the boundary condition is free-space, the exchange correlation functional is LDA, The boundary condition is free-space, and the simulation cell cell is aperiodic and cubic with a side length of 10.0 Angstroms and has 40 grid points in each direction (cutoff energy is 44 Ry). The time step and fake mass for the Car-Parrinello run are specified to be 5.0 au and 600.0 au, respectively. 

         
start c2_pspw_lda_md
title "C2 restricted singlet dimer, LDA/44Ry - constant energy Car-Parrinello simulation"

geometry  
C    -0.62 0.0 0.0
C     0.62 0.0 0.0
end
       
pspw
   simulation_cell units angstroms
      boundary_conditions aperiodic
      lattice
        lat_a 10.00d0
        lat_b 10.00d0
        lat_c 10.00d0
      end
      ngrid 40 40 40
   end
   Car-Parrinello
     fake_mass 600.0
     time_step 5.0
     loop 10 10
   end
end
set nwpw:minimizer 2
task pspw energy
task pspw Car-Parrinello


35.9 PSPW Tutorial 3: Running a Simulated Annealing Car-Parrinello Simulation


35.10 PSPW Tutorial 4: optimizing a unit cell and geometry for Silicon-Carbide

The following example demonstrates how to uses the PSPW module to optimize the unit cell and geometry for a silicon-carbide crystal. 

title "SiC 8 atom cubic cell - geometry and unit cell optimization"

start SiC

#**** Enter the geometry using fractional coordinates ****
geometry units au center noautosym noautoz print
  system crystal
    lat_a 8.277d0
    lat_b 8.277d0
    lat_c 8.277d0
    alpha 90.0d0
    beta  90.0d0
    gamma 90.0d0
  end
Si    -0.50000d0  -0.50000d0  -0.50000d0
Si     0.00000d0   0.00000d0  -0.50000d0
Si     0.00000d0  -0.50000d0   0.00000d0
Si    -0.50000d0   0.00000d0   0.00000d0
C     -0.25000d0  -0.25000d0  -0.25000d0
C      0.25000d0   0.25000d0  -0.25000d0
C      0.25000d0  -0.25000d0   0.25000d0
C     -0.25000d0   0.25000d0   0.25000d0
end

#***** setup the nwpw gamma point code ****
nwpw
   simulation_cell
     ngrid 16 16 16
   end
   ewald_ncut 8
end
set nwpw:minimizer 2
set nwpw:psi_nolattice .true.  # turns of unit cell checking for wavefunctions

driver
  clear
  maxiter 40
end
set includestress .true.    # this option tells driver to optimize the unit cell

task pspw optimize


35.11 Band Tutorial 1: Minimizing the energy of a silicon-carbide crystal by running a PSPW and Band simulation in tandem

The following input deck performs a PSPW energy calculation followed by a Band energy calculation at the $\Gamma$-point for a cubic (8-atom) silicon-carbide crystal. Since the geometry is entered using fractional coordinates the unit cell parameters do not have to be re-specified in the simulation_cell nwpw sub-block. In this example, default pseudopotential from the pseudopotential library are used for C and Si. The advantage of running these calculations in tandem is that the Band code uses the wavefunctions generated from the faster PSPW calculation for its initial guess. The PSPW energy is -38.353570, and the Band energy is -38.353570. 

start SiC_band
title "SiC 8 atom cubic cell"

#**** geometry entered using fractional coordinates ****
geometry units au center noautosym noautoz print 
  system crystal 
    lat_a 8.277d0
    lat_b 8.277d0
    lat_c 8.277d0
    alpha 90.0d0
    beta  90.0d0
    gamma 90.0d0
  end
Si    -0.50000d0  -0.50000d0  -0.50000d0
Si     0.00000d0   0.00000d0  -0.50000d0
Si     0.00000d0  -0.50000d0   0.00000d0
Si    -0.50000d0   0.00000d0   0.00000d0
C     -0.25000d0  -0.25000d0  -0.25000d0
C      0.25000d0   0.25000d0  -0.25000d0
C      0.25000d0  -0.25000d0   0.25000d0
C     -0.25000d0   0.25000d0   0.25000d0
end

#***** setup the nwpw gamma point code ****
nwpw
   simulation_cell
     ngrid 16 16 16
   end
   brillouin_zone
     kvector  0.0 0.0 0.0
   end
   ewald_ncut 8
end
set nwpw:minimizer 2
set nwpw:psi_brillioun_check .false.
task pspw energy
task band energy


35.12 PAW Tutorial

The following input deck performs for a water molecule a PSPW energy calculation followed by a PAW energy calculation and a PAW geometry optimization calculation. The default unit cell paramters are used (SC=20.0, ngrid 32 32 32). In this simulation, the first PAW run optimizes the wavefunction and the second PAW run optimizes the wavefunction and geometry in tandem. 

title "paw steepest descent test"

start paw_test

charge 0

geometry units au nocenter noautoz noautosym
O      0.00000    0.00000    0.01390
H     -1.49490    0.00000   -1.18710
H      1.49490    0.00000   -1.18710
end

nwpw
   time_step 15.8
   ewald_rcut 1.50
   tolerances 1.0d-8 1.0d-8
end
set nwpw:lcao_iterations 1
set nwpw:minimizer 2
task pspw energy

task paw steepest_descent

nwpw
   time_step 5.8
   geometry_optimize
   ewald_rcut 1.50
   tolerances 1.0d-7 1.0d-7 1.0d-4
end
task paw steepest_descent


35.13 NWPW Capabilities and Limitations

35.14 Questions and Difficulties

Questions and encountered problems should be reported to nwchem-support@emsl.pnl.gov or to Eric J. Bylaska, Eric.Bylaska@pnl.gov

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2003-10-08