# 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
- Electric field gradients with relativistic effects
- 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
- Gshift
- Response to electric and magnetic fields (static and dynamic)
- Raman

The properties module is started when the task directive TASK

```
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 hyperfine and indirect spin-spin coupling require a UHF or ODFT wave function.

## Vectors keyword¶

```
VECTORS [ (<string input_movecs >)]
```

The VECTORS directive allows the user to specify the input molecular orbital vectors for the property calculation

## Property keywords¶

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

```
NBOFILE
DIPOLE
QUADRUPOLE
OCTUPOLE
MULLIKEN
ESP
EFIELD
EFIELDGRAD
EFIELDGRADZ4
GSHIFT
ELECTRONDENSITY
HYPERFINE [<integer> number_of_atoms <integer> atom_list]
SHIELDING [<integer> number_of_atoms <integer> atom_list]
SPINSPIN [<integer> number_of_pairs <integer> pair_list]
RESPONSE [<integer> response_order <real> frequency]
AIMFILE
MOLDENFILE
ALL
```

The “ALL” keyword generates all currently available properties.

### NMR and EPR¶

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 chosen for each atom under consideration.

**Calculating EPR and paramagnetic NMR parameters:** The following
tutorial illustrates how to combine the
hyperfine, gshift and shielding to calculate the EPR and paramagnetic
NMR parameters of an open-shell system. All calculations are compatible
with the ZORA model potential approach.

For theoretical and computational details, please refer to the following references:

- J. Autschbach, S. Patchkovskii, B. Pritchard, “Calculation of Hyperfine Tensors and Paramagnetic NMR Shifts Using the Relativistic Zeroth-Order Regular Approximation and Density Functional Theory”, Journal of Chemical Theory and Computation 7, 2175 (2011)
- F. Aquino, B. Pritchard, J. Autschbach, “Scalar relativistic computations and localized orbital analysis of nuclear hyperfine coupling and paramagnetic NMR chemical shifts”, J. Chem. Theory Comput. 2012, 8, 598–609.
- F. Aquino, N. Govind, J. Autschbach, “Scalar relativistic computations of nuclear magnetic shielding and g-shifts with the zeroth-order regular approximation and range-separated hybrid density functionals”, J. Chem. Theory Comput. 2011, 7, 3278–3292.

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.

### Response Calculations¶

Response calculations can be calculated as follows:

```
property
response 1 7.73178E-2 # response order and frequency in Hartree energy units
velocity # use modified velocity gauge for electric dipole
orbeta # calculate optical rotation 'beta' directly [2]
giao # GIAO optical rotation [1,3,6], forces orbeta
bdtensor # calculates B-tilde of Refs. [1,6]
analysis # analyze response in terms of MOs [6]
damping 0.007 # complex response functions with damping, Ref [5]
convergence 1e-4 # set CPKS convergence criterion (default 1e-4)
end
```

Response calculations are currently supported only for order 1 (linear response), single frequency, electric field and mixed electric-magnetic field perturbations. The output consists of the electric polarizability and optical rotation tensors (alpha, beta for optical rotation) in atomic units. If the ‘velocity’ or ‘giao’ keywords are absent, the dipole-length form will be used for the dipole integrals. This is a bit faster. The isotropic optical rotation is origin independent when using the velocity gauge or with GIAOs [1]. With the keyword ‘bdtensor’, a fully origin-invariant optical rotation tensor is calculated [1,6]. Note that ‘velocity’ and ‘orbeta’ are incompatible. An input line ‘set prop:newaoresp 0’ outside of the ‘properties’ block forces the use of an older version of the response code, which has fewer features (in particular, no working GIAO opetical rotation) but which has been tested more thoroughly. In the default newer version you may encounter undocumented features (bugs). ‘analysis’ triggers an analysis of the response tensors in terms of molecular orbitals. If the property input block also contains the keyword ‘pmlocalization’, then the analysis is performed in terms of Pipek-Mezey localized MOs, otherwise the canonical set is used (this feature may currently not work, please check the sum of the analysis carefully). See Ref. [6] for an example. Works with HF and density functionals for which linear response kernels are implemented in NWChem.

Please refer to the following papers for further details:

- J. Autschbach, ChemPhysChem 12 (2011), 3224-3235
- J. Autschbach, Comp. Lett. 3, (2007), 131
- M. Krykunov, J. Autschbach, J. Chem. Phys. 123 (2005), 114103
- J.R. Hammond, N. Govind, K. Kowalski, J. Autschbach, S.S. Xantheas, J. Chem. Phys. 131 (2009), 214103
- M. Krykunov, M. D. Kundrat, J. Autschbach, J. Chem. Phys. 125 (2006), 194110
- B. Moore II, M. Srebro, J. Autschbach, J. Chem. Theory Comput. 8 (2012), 4336-4346

### Raman¶

Raman calculations can be performed by specifying the Raman block. These calculations are performed in conjunction with polarizability calculations. Detailed description of input parameters at http://pubs.acs.org/doi/suppl/10.1021/jp411039m

```
RAMAN
[ (NORMAL | | RESONANCE) default NORMAL ]
[ (LORENTZIAN | | GAUSSIAN) default LORENTZIAN ]
[ LOW <double low default 0.0> ]
[ HIGH <double high default highest normal mode> ]
[ FIRST <integer first default 7> ]
[ LAST < integer last default number of normal modes > ]
[ WIDTH <double width default 20.0> ]
[ DQ <double dq default 0.01> ]
END
task dft raman
```

or

```
task dft raman numerical
```

Sample input block:

```
property
response 1 8.8559E-2
damping 0.007
end
raman
normal
lorentzian
end
```

#### Raman Keywords¶

- NORMAL and RESONANCE: Type of Raman plot to make.
- LORENTZIAN and GAUSSIAN: Generation of smoothed spectra (rather than sticks) using either a Lorentzian function or a Gaussian function. The default is LORENTZIAN.
- LOW and HIGH: The default range in which to generate the Raman spectrum plot is (0.0, highest wavenumber normal mode) cm-1. The LOW and HIGH keywords modify the frequency range.
- FIRST and LAST: The default range of indices of normal modes used in the plot is (7, number of normal modes). The FIRST and LAST keywords modify the range of indices.
- WIDTH:Controls the width in the smoothed peaks, using Lorentzians or Gaussians, in the plot. The default value for WIDTH is 20.0.
- DQ: Size of the steps along the normal modes. The default value for DQ is 0.01. It is related to the step size dR used in numerical evaluation of polarizability derivative

#### Raman Output¶

Raman spectrum in stick format and smoothed using Lorentzians or
Gaussians stored in a filename with format [fname].normal.

The number of points is 1000 by default. This value can be changed by adding the following SET directive to the input file

```
set raman:numpts <integer>
```

#### Raman References¶

Please refer to the following papers for further details:

- J. M. Mullin, J. Autschbach, G. C. Schatz, Computational and Theoretical Chemistry 987, 32 (2012). DOI: 10.1016/j.comptc.2011.08.027.
- F. W. Aquino and G. C. Schatz, The Journal of Physical Chemistry A 118 , 517 (2014). DOI: 10.1021/jp411039m

### 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,

Users that have their own NBO version can compile and link the code into the NWChem software. See the INSTALL file in the source for details.

## Gaussian Cube Files¶

Electrostatic potential (keyword *esp*) and the magnitude of the
electric field (keyword *efield*) on the grid can be generated in the
form of the Gaussian Cube File. This behavior is triggered by the
inclusion of grid keyword as shown
below

```
grid [pad dx [dy dz]] [rmax x y z] [rmin x y z] [ngrid nx [ny nz]] [output filename]
```

where

- pad dx [dy dz] - specifies amount of padding (in angstroms) in x,y, and z dimensions that will be applied in the automatic construction of the rectangular grid volume based on the geometry of the system. If only one number is provided then the same amount of padding will be applied in all dimensions. The default setting is 4 angstrom padding in all dimensions.

- rmin x y z - specifies the coordinates (in angstroms) of the minimum corner of the rectangular grid volume. This will override any padding in this direction.

- rmax x y z - specifies the coordinates (in angstroms) of the maximum corner of the rectangular grid volume. This will override any padding in this direction.

- ngrid nx [ny nz] - specifies number of grid points along each dimension. If only one number is provided then the same number of grid points are assumed all dimensions. In the absence of this directive the number of grid points would be computed such that grid spacing will be close to 0.2 angstrom, but not exceeding 50 grid points in either dimension.

- output filename - specifies name of the output cube file. The
default behavior is to use \<prefix>-elp.cube or \<prefix>-elf.cube
file names for electrostatic potential or electric field
respectively. Here
denotes the system name as specified in start directive. Note that Gaussian cube files will be written in the run directory (where the input file resides).

Example input file

```
echo
start nacl
geometry nocenter noautoz noautosym
Na -0.00000000 0.00000000 -0.70428494
Cl 0.00000000 -0.00000000 1.70428494
end
basis
* library 6-31g*
end
#electric field would be written out to nacl.elf.cube file
#with
#ngrid : 20 20 20
#rmax : 4.000 4.000 5.704
#rmin :-4.000 -4.000 -4.704
property
efield
grid pad 4.0 ngrid 20
end
task dft property
#electrostatic potential would be written to esp-pad.cube file
# with the same parameters as above
property
esp
grid pad 4.0 ngrid 20 output esp-pad.cube
end
task dft property
#illustrating explicit specification of minumum box coordinates
property
esp
grid pad 4.0 rmax 4.000 4.000 5.704 ngrid 20
end
task dft property
```

## Aimfile¶

This keyword generates AIM Wavefunction files. The resulting AIM wavefunction file (.wfn/.wfx) can be post-processed with a variety of codes, e.g.

More details at
https://sites.google.com/site/alvarovazquezmayagoitia/goals/codes/nwchem-notes/generator-of-aim-wavefunction-files-nwchem

**WARNING:** Since we have discovered issues in generating .WFN files with this module (e.g. systems with ECPs), the recommended method for generating .WFN file is to first generate a Molden file with the Moldenfile option, then convert the Molden file into a WFN file by using the Molden2AIM program.

## Moldenfile¶

```
MOLDENFILE
MOLDEN_NORM (JANPA | | NWCHEM || NONE)
```

This keyword generates files using the Molden format. The resulting Molden file (.molden) should compatible with a variety of codes that can input Molden files, e.g.

- Molden
- JANPA (the nwchem2molden step is no longer
required when using .molden files and the
`MOLDEN_NORM JANPA`

keyword) - orbkit
- Molden2qmc
- Molden2AIM
- Multiwfn

the `MOLDEN_NORM`

option allows the renormalization of the basis set
coefficients. By default, the coefficient values from input are not
modified. Using the `JANPA`

value coefficients are normalized following
JANPA‘s
convention, while the `NWCHEM`

will produce coefficients normalized
according to NWChem’s convention. Using `MOLDEN_NORM`

equal `NONE`

will
leave the input coefficients unmodified.

It is strongly recommended to use **spherical** basis set when using the NWChem Molden output for JANPA analysis

Example input file for a scf calculation. The resulting Molden file will
be named `h2o.molden`

```
start heat
geometry; he 0. 0. 0.; end
basis spherical; * library 6-31g ; end
task scf
property
vectors heat.movecs
moldenfile
molden_norm janpa
end
task scf property
```

Then, the resulting `h2o.molden`

file can be post processed by Janpa with the following command

```
java -jar janpa.jar h2o.molden > h2o.janpa.txt
```