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116 lines
4.3 KiB
TeX
116 lines
4.3 KiB
TeX
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% $Id$
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%
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\label{sec:property}
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Properties can be calculated for both the Hartree-Fock and DFT wave
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functions. The properties that are available are:
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\begin{itemize}
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\item Natural bond analysis
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\item Dipole, quadrupole, and octupole moment
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\item Mulliken population analysis and bond order analysis
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\item Electrostatic potential (diamagnetic shielding) at nuclei
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\item Electric field and field gradient at nuclei
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\item Electron and spin density at nuclei
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\item NMR shielding (GIAO method)
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\item NMR hyperfine coupling (Fermi-Contact and Spin-Dipole expectation values)
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\item NMR indirect spin-spin coupling
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\end{itemize}
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The properties module is started when the task directive
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\verb+TASK <theory> property+ is defined in the user input file. The input
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format has the form:
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\begin{verbatim}
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PROPERTY
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[property keyword]
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[CENTER ((com || coc || origin || arb <real x y z>) default coc)]
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END
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\end{verbatim}
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Most of the properties can be computed for Hartree-Fock
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(closed-shell RHF, open-shell ROHF, and open-shell UHF), and DFT
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(closed-shell and open-shell spin unrestricted) wavefunctions. The NMR
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chemical shift is limited to closed-shell wave functions, whereas the NMR
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hyperfine and indirect spin-spin coupling require a UHF or ODFT wave function.
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\section{Property keywords}
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Each property can be requested by defining one of the following keywords:
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\begin{verbatim}
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NBOFILE
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DIPOLE
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QUADRUPOLE
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OCTUPOLE
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MULLIKEN
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ESP
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EFIELD
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EFIELDGRAD
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ELECTRONDENSITY
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HYPERFINE
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SHIELDING [<integer> number_of_atoms <integer> atom_list]
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SPINSPIN [<integer> number_of_pairs <integer> pair_list]
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AIMFILE
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ALL
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\end{verbatim}
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The ``{\tt ALL}'' keyword generates all currently available properties.
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Both the NMR shielding and spin-spin coupling have additional optional
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parameters that can be defined in the input. For the shielding the user
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can define the number of atoms for which the shielding tensor should be
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calculated, followed by the list of specific atom centers. In the case
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of spin-spin coupling the number of atom pairs, followed by the atom
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pairs, can be defined (i.e., spinspin 1 1 2 will calculate the coupling
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for one pair, and the coupling will be between atoms 1 and 2).
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For both the NMR spin-spin and hyperfine coupling the isotope that has
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the highest abundance and has spin, will be choosen for each atom under
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consideration.
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The user also has the option to choose the center of expansion for
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the dipole, quadrupole, and octupole calculations.
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\begin{verbatim}
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[CENTER ((com || coc || origin || arb <real x y z>) default coc)]
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\end{verbatim}
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\verb+com+ is the center of mass, \verb+coc+ is the center of charge, \verb+origin+ is
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(0.0, 0.0, 0.0) and \verb+arb+ is any arbitrary point which must be accompanied
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by the coordinated to be used. Currently the x, y, and z coordinates
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must be given in the same units as \verb+UNITS+ in \verb+GEOMETRY+ (See Section
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\ref{sec:geomkeys}).
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\subsection{Nbofile}
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\label{sec:Nbofile}
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The keyword {\tt NBOFILE} does not execute the Natural Bond Analysis
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code, but simply creates an input file to be used as input to the
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stand-alone NBO code. All other properties are calculated upon
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request.
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Following the successful completion of an electronic structure
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calculation, a Natural Bond Orbital (NBO) analysis may be carried out
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by providing the keyword \verb+NBOFILE+ in the \verb+PROPERTY+ directive.
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NWChem will query the rtdb and construct an ASCII file,
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\verb+<file_prefix>.gen+, that may be used as input to the stand alone
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version of the NBO program, gennbo. \verb+<file_prefix>+ is equal to
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string following the \verb+START+ directive. The input deck may be edited
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to provide additional options to the NBO calculation, (see the NBO
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user's manual for details.)
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\subsection{AIM file}
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\label{sec:AIMfile}
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The keyword {\tt aimfile} creates a \verb+.wfn+ file from a given
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eigenvector file (i.e., \verb+.movecs+), geometry and a basis set.
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The \verb+.wfn+ file summarizes the single determinant wavefunction in order to be analyzed
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through a third-party software.
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Among some known analyses are the Bader's approach for atoms in molecules (AIM), the electron
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localization function (ELF), the Fermi hole function and energy density analysis.
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The follow input directive will create the an AIM file \verb+.wfx+ format.
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\begin{verbatim}
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set prop:nowfx F
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\end{verbatim}
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