# 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

tddft

None

Enable time-dependent DFT

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.