28. Properties

Properties can be calculated for both the Hartree-Fock and DFT wave functions. The properties that are available are:

• Natural bond analysis
• Dipole, quadrupole, and octupole moment
• Mulliken population analysis and bond order analysis
• Electrostatic potential (diamagnetic shielding) at nuclei
• Electric field and field gradient at nuclei
• Electron and spin density at nuclei
• NMR shielding (GIAO method)
• NMR hyperfine coupling (Fermi-Contact and Spin-Dipole expectation values)
• NMR indirect spin-spin coupling

The properties module is started when the task directive TASK <theory> property is defined in the user input file. The input format has the form:

  PROPERTY
    [property keyword]
    [CENTER ((com || coc || origin || arb <real x y z>) default coc)]
  END

Most of the properties can be computed for Hartree-Fock (closed-shell RHF, open-shell ROHF, and open-shell UHF), and DFT (closed-shell and open-shell spin unrestricted) wavefunctions. The NMR chemical shift is limited to closed-shell wave functions, whereas the NMR hyperfine and indirect spin-spin coupling require a UHF or ODFT wave function.

28.1 Property keywords

Each property can be requested by defining one of the following keywords:

  NBOFILE
  DIPOLE
  QUADRUPOLE
  OCTUPOLE
  MULLIKEN
  ESP
  EFIELD
  EFIELDGRAD
  ELECTRONDENSITY
  HYPERFINE
  SHIELDING [<integer> number_of_atoms <integer> atom_list]
  SPINSPIN [<integer> number_of_pairs <integer> pair_list]
  ALL

The ``ALL'' keyword generates all currently available properties.

Both the NMR shielding and spin-spin coupling have additional optional parameters that can be defined in the input. For the shielding the user can define the number of atoms for which the shielding tensor should be calculated, followed by the list of specific atom centers. In the case of spin-spin coupling the number of atom pairs, followed by the atom pairs, can be defined (i.e., spinspin 1 1 2 will calculate the coupling for one pair, and the coupling will be between atoms 1 and 2).

For both the NMR spin-spin and hyperfine coupling the isotope that has the highest abundance and has spin, will be choosen for each atom under consideration.

The user also has the option to choose the center of expansion for the dipole, quadrupole, and octupole calculations.

    [CENTER ((com || coc || origin || arb <real x y z>) default coc)]

com is the center of mass, coc is the center of charge, origin is (0.0, 0.0, 0.0) and arb is any arbitrary point which must be accompanied by the coordinated to be used. Currently the x, y, and z coordinates must be given in the same units as UNITS in GEOMETRY (See Section 6.1).

28.1.1 Nbofile

The keyword NBOFILE does not execute the Natural Bond Analysis code, but simply creates an input file to be used as input to the stand-alone NBO code. All other properties are calculated upon request.

Following the successful completion of an electronic structure calculation, a Natural Bond Orbital (NBO) analysis may be carried out by providing the keyword NBOFILE in the PROPERTY directive. NWChem will query the rtdb and construct an ASCII file, <file_prefix>.gen, that may be used as input to the stand alone version of the NBO program, gennbo. <file_prefix> is equal to string following the START directive. The input deck may be edited to provide additional options to the NBO calculation, (see the NBO user's manual for details.)