NWChem

NWChem is a computational chemistry code based on gaussian basis functions or plane-waves.

Setup

You first need to install a working copy of NWChem for ASE to call; follow the instructions on the NWChem website.

The default command that ASE will use to start NWChem is nwchem PREFIX.nw > PREFIX.out. You can change this command by setting the environment variable ASE_NWCHEM_COMMAND. (For example, add a line to your .bashrc with export ASE_NWCHEM_COMMAND="my new command".)

The default command will only allow you to run NWChem on a single core. To run on multiple processors you will need to specify your MPI (or similar) command, which typically requires telling the MPI command the number of tasks to dedicate to the process. An example command to allow multiprocessing is mpirun -n $SLURM_NTASKS nwchem PREFIX.nw > PREFIX.out, for the SLURM queueing system. If you use a different queueing system replace $SLURM_NTASKS with the appropriate variable, such as $PBS_NP.

Examples

Here is a command line example of how to optimize the geometry of a water molecule using the PBE density functional:

$ ase build H2O | ase run nwchem -p xc=PBE -f 0.02
Running: H2O
LBFGS:   0  09:58:54    -2064.914841       1.9673
LBFGS:   1  09:58:55    -2064.976691       0.1723
LBFGS:   2  09:58:55    -2064.977120       0.0642
LBFGS:   3  09:58:55    -2064.977363       0.0495
LBFGS:   4  09:58:56    -2064.977446       0.0233
LBFGS:   5  09:58:56    -2064.977460       0.0059
$ ase gui H2O.traj@-1 -tg "a(1,0,2),d(0,1)"
102.591620591 1.00793234388

An example of creating an NWChem calculator in the python interface is:

from ase.calculators.nwchem import NWChem

calc = NWChem(label='calc/nwchem',
              maxiter=2000,
              xc='B3LYP',
              basis='6-31+G*')

If you need to request more memory, it is typically not sufficient to do so only through your queuing system. You need to also let NWChem know about the additional available memory, with NWChem’s \(memory\) keyword which in turn is added through ASE’s \(raw\) keyword (which puts raw text lines in the NWChem input file). An example is below; see the official NWChem documentation for the proper use of the \(memory\) keyword.

calc = NWChem(label='calc/nwchem',
              raw='memory 2000 MB')

Parameters

The list of possible parameters and their defaults is shown below. See the NWChem documentation for full explanations of these different options.

keyword type default value description
label str 'nwchem' Label for saved files.
xc str 'LDA' Exchange-correlation functional.
smearing   None Smearing.
charge   None Charge
task str 'gradient' Task to perform. ‘gradient’ means force call.
geometry str 'nocenter noautosym' Geometry arguments. Note NWChem centers the coordinates by default.
convergence dict   Convergence criteria.
basis str '3-21G' Basis set.
print str None Flags within the DFT block steering the output details.
basispar   None  
ecp   None  
so   None  
spinorbit   None Use spin-orbit DFT module.
odft   None Use open-shell (spin-polarized) DFT.
raw   '' Raw text outside DFT block control string.

See the source code link below for further details.

class ase.calculators.nwchem.NWChem(restart=None, ignore_bad_restart_file=False, label='nwchem', atoms=None, **kwargs)[source]

Construct NWchem-calculator object.