Gaussian
========

From the Gaussian website gaussian.com:

    Gaussian 16 is the latest version of the Gaussian series of electronic structure programs, used by chemists, chemical engineers, biochemists, physicists and other scientists worldwide.

Accessing Gaussian on CSD3
--------------------------

Cambridge holds a site licence for Gaussian, so the gaussian installs can be used by any Cambridge accademic user. To request that your account on CSD3 be added to the ``gaussian`` group please contact support@hpc.cam.ac.uk.

Running Gaussian
----------------

A sample job for Gaussian09 (a relatively old version) requires a simple job script::

    #!/bin/bash
    #SBATCH -J g09test
    #SBATCH -A MYACCOUNT -p skylake
    #SBATCH -N 1 -n 1 -c 16
    #SBATCH -t 1:00:00

    module load gaussian/09
    g09 dimer4.com dimer4.out

which tells gaussian to read input from ``dimer4.com`` and write to ``dimer4.out``. The ``dimer4.com`` could be::

    %Mem=3800MB
    %NProcShared=16
    %Chk=dimer4.chk
    #P MP2 aug-cc-pVTZ SCF=Tight

    methanol dimer MP2

    0 1
    6 0.754746 -0.733607 -0.191063
    1 -0.033607 -1.456810 -0.395634
    1 1.007890 -0.778160 0.867678
    1 1.635910 -0.998198 -0.774627
    8 0.317192 0.576306 -0.534002
    1 1.033100 1.188210 -0.342355
    6 1.513038 3.469264 0.971885
    1 1.118398 2.910304 1.819367
    1 0.680743 3.818664 0.361783
    1 2.062618 4.333044 1.344537
    8 2.372298 2.640544 0.197416
    1 2.702458 3.161614 -0.539550

(note there must be a blank line at the end of the input file). Gaussian supports running in shared memory parallel mode, which is configured via the options ``-c`` to slurm and ``%NProcShared`` to Gaussian itself. These two numbers should match, and on our skylake hardware one can use up to the whole 32 cores on a compute node. Running across multiple nodes requires the Linda package.

The ``%Ckk=`` directive instructs Gaussian to produce checkpoint files in order, saving the intermediate state of a calcaultion. This is useful both for checking the intermediate results, and also for restarting failed calulcations (for example if a job runs out of walltime and ends prematurely).

Running GaussView
-----------------

The GaussView application is available in a module ``gaussview/6``. This will work best when run from one of the login nodes configured with graphics hardware (login-gfx1 and login-gfx2), and when run under the virtualGL environment with ``vglrun gview``.