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.. module:: ase.calculators.nwchem
======
NWChem
======
`NWChem <https://nwchemgit.github.io>`_ is a computational chemistry code
based on gaussian basis functions or plane-waves.
Setup
=====
.. highlight:: bash
You first need to install a working copy of NWChem for ASE to call;
follow the instructions on the `NWChem website <https://nwchemgit.github.io>`_.
The default command that ASE will use to start NWChem is
``nwchem PREFIX.nwi > PREFIX.nwo``. You can change this command by setting the
environment variable :envvar:`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 $SLURM_NTASKS nwchem PREFIX.nwi > PREFIX.nwo``, for the SLURM
queueing system. If you use a different queueing system replace
``$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
.. highlight:: python
An example of creating an NWChem calculator in the python interface is::
from ase.calculators.nwchem import NWChem
calc = NWChem(label='calc/nwchem',
dft=dict(maxiter=2000,
xc='B3LYP'),
basis='6-31+G*')
Parameters
==========
.. highlight:: none
The NWChem calculator represents nested keyword blocks in the input file using
nested Python dictionaries. For example, consider the following block of input::
memory 1024 mb
dft
xc B3LYP
mult 2
odft
convergence energy 1e-5 density 1e-4 gradient 5e-3
end
.. highlight:: python
This would be represented by the following keyword arguments to the NWChem
calculator::
NWChem(memory='1024 mb',
dft=dict(xc='B3LYP',
mult=2,
odft=None,
convergence=dict(energy=1e-5,
density=1e-4,
gradient=5e-3),
),
)
Most input files can be constructed in this way. The NWChem calculator also
has several special keywords which do not directly enter into the input file;
these are described in the table below
============== ======== =============== ==================================================
keyword type default value description
============== ======== =============== ==================================================
``label`` ``str`` ``'nwchem'`` Used to name input and output files. Also,
used as the default name of the perm and
scratch directory, unless otherwise
specified.
``theory`` ``str`` See description Theory specifies the kind of calculation
you want to do. Currently supported
values are ``dft``, ``scf``, ``mp2``,
``ccsd``, ``tce``, ``tddft``, ``pspw``,
``band``, and ``paw``. Other settings
may work, but have not been tested.
If not provided, the Calculator will
attempt to guess based on the provided
keywords.
``center`` ``bool`` ``False`` Whether NWChem should automatically
center your atoms. You probably
don't want to change this.
``autosym`` ``bool`` ``False`` Whether NWChem should automatically
symmetrize your atoms. You probably
don't want to change this.
``autoz`` ``bool`` ``False`` Whether NWChem should automatically
generate a Z-matrix for your system.
``basis`` ``str`` ``3-21G`` If provided with a string, the
specified basis set will be used for
all atoms. Alternatively, you can set
element-specific basis sets by passing
a dict, e.g. ``basis=dict(C='6-31G', O='3-21G')``.
``basispar`` ``str`` ``''`` Additional keywords to go in the
first line of the ``basis`` block.
``task`` ``str`` See description What kind of calculation is to be
performed, e.g. ``'energy'``,
``'gradient'``, or ``'optimize'``.
If not provided, it will be
automatically determined by the
Calculator.
``symmetry`` ``str`` ``''`` The symmetry group or number of your
system.
``geompar`` ``str`` ``''`` Additional keywords to go in the first
line of the ``geometry`` block.
``set`` ``dict`` ``dict()`` A set of keys and values to be added
directly to the NWChem rtdb. This
isn't necessary for most commonly
done tasks, but it is required for
certain functionality in plane-wave
mode.
``restart_kw`` ``str`` ``'start'`` If set to ``'restart'``, then the calculation
will attempt to restart from whatever
restart files are available as
specified in the .db file (may need to
be combined with other keywords).
============== ======== =============== ==================================================
.. autoclass:: NWChem
|
