28. Properties

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

Calculation of properties is accomplished with TASK PROPERTY after the completion of an energy (or MP2 gradient) calculation. The following properties can be computed for all wavefunctions that produce orbitals, including Hartree-Fock (closed-shell RHF, open-shell ROHF, and open-shell UHF), DFT (closed-shell and open-shell spin unrestricted), MCSCF (complete active space), and MP2 (closed-shell RHF and open-shell UHF).

• natural bond analysis
• dipole moment
• quadrupole moment
• octupole moment
• Mulliken population analysis and bond order analysis
• electrostatic potential (diamagnetic shielding) at nuclei
• electric field at nuclei
• electric field gradient at nuclei
• electron and spin density at nuclei
• NMR chemical shifts (GIAO method) only for closed-shell RHF

The default molecular orbital file $file_prefix$.movecs is used unless a vectors directive (Section 10.5) is provided. It is therefore only necessary to include a vectors directive if the MO vectors to be analyzed are not coming from the default file, e.g., if they have been previously redirected, or if MP2 natural orbitals (file extension ".mp2nos") are being anaylzed. The MP2 natural orbitals MUST be used if the user wants MP2 properties.

28.1 Subdirectives

Note that presenting any property input causes all previous property input to be ``forgotten'', unlike other NWChem modules.

Each property can be requested by means of a subdirective among the subdirectives provided :

• NBOFILE
• DIPOLE
• QUADRUPOLE
• OCTUPOLE
• MULLIKEN
• ESP
• EFIELD
• EFIELDGRAD
• ELECTRONDENSITY
• GIAO
• ALL

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

The request 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. To execute the NBO analysis directly, see Section 37.1. All other properties are calculated upon request.

An additional subdirective is provided to specify the origin of the molecular orbitals used in the calculation of the molecular properties. This is the `VECTORS' subdirective, also used in the SCF and DFT tasks. For a full description of this subdirective the user is refered to the description found in the SCF description. By default, the input file used for the calculation of the properties has the .movecs name extension.

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

Following the successful completion of an electronic structure calculation, a Natural Bond Orbital (NBO) analysis may be carried out in the following way. On restart specify the TASK as PROPERTY and supply the sub-directive NBOFILE to 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 RESTART directive. The input deck may be edited to provide additional options to the NBO calculation, (see the NBO user's manual for details.) The other option in to directly run the NBO analysis (See Section 37.1 for more information).