GAMESS

GAMESS (General Atomic and Molecular Electronic Structure System) is a program designed to carry out quantum chemical calculations. The current version of GAMESS at NERSC is that released in June 2002 by the Chemistry Department at Iowa State University.

Setup

The modules package controls access to software. To use GAMESS:

% module load gamess

This commnd may also be included in a script which runs an GAMESS job.

Running GAMESS

GAMESS is most easily run with the prungms command for parallel GAMESS or srungms command for serial GAMESS. These commands takes care of setting the various environment variables and Loadleveler parameters required to connect files.

The format of the prungms command is:

% prungms -l logfile -n nodes -t hh:mm -c class -s dir job

where job is the name of your input file, which must have a suffix ".inp". The arguments are described below:

-l logfile

where logfile gives the output/log file name

-n nodes

where nodes gives the number of nodes, there will be 16 computes processes per node

-t time

where time gives the wall clock time limit, and must be of the form hh:mm

-c class

where class gives the Loadleveler class for the job

-s dir

where dir gives the scratch directory for the job

All arguments are optional. You will be prompted for required arguments (with defaults available) if you leave them off. The command will then submit a job to Loadleveler. The dir option is a directory relative to the directory$SCRATCH/gms. This directory will be created for you if it does not exist.

The srungms script is identical to prungms, except that it does not take the "-n" option since it submits a serial job.

Electronic Structure Methods Available

The following table shows the options available for each calculation and scf type. The key is as follows: C indicates "conventional" (disk-based) integral storage; D indicates direct-integral method; P indicates parallel operation.

Resource Usage

For conventional algorithms, the disk space required will grow very rapidly with the size of the system. For these cases it would be better to use the integral-direct algorithm. The prungms command generates a new scratch directory, as a subdirectory of $SCRATCH/gms, for each run. Periodically you should remove these directories as they will consume disk space counted against your quota.

By default GAMESS allocates 8 MB of memory. If you increase the amount of memory to be allocated by using the MEMORY, MWORDS, or MEMDDI parameter in the $SYSTEM input group, you should take care not to exceed the physical memeory (usually 32 GB) of the nodes you are running on.

Parallel Operation

GAMESS has a somewhat complicated method of parallel operation. For an N way parallel job, 2 × N MPI processes are required. Half of these processes perform data-handling only, while the other half do computation. Because of this, a nonstandard way of allocating and using MPI tasks is employed that enables 16 MPI tasks to be run on one bassi node. Chapter 5 of the documentation describes this in detail.

Help

The GAMESS Home Page contains an up-to-date resource for tutorials, documentation, and discussion groups.