Difference between revisions of "HowTo:gaussian"

Features

Gaussian does electronic-structure calculations and standard quantum chemical calculations. Among the methods available are simple molecular mechanics (such as Amber force field), semi-empirical methods (such as CNDO), Hartree-Fock (restricted and unrestricted), MPn (Mollar-Plesset perturbation theory of order n=2,3,4), CI (Configuration-Interaction), CC (Coupled-Cluster), Multi-configurational SCF (such as CAS-SCF) and various DFT (Density-Functional Theory) methods. Specific to Gaussian are high-accuracy energy methods (G2, CBS). It can be used to obtain electronic properties, molecular geometries, vibrational frequencies, orbitals, reaction profiles, and much more. Check out the capabilities here.

Location of the program and setup

The program resides in /global/software/gaussian. Multiple versions and revisions of the program are located in different sub-directories. The name of the root executable is g16.

The source code of Gaussian is not publicly accessible since Gaussian is a licensed product. However, Gaussian grants the permission to alter the code under certain conditions. If you want to do so, contact us to learn more. You are not allowed to copy the executable or any part of the distribution onto your local machine.

On Frontenac, we are using the module (lmod) system to set up Gaussian. This means that typing

 module load gaussian 

is automatically adding all required settings to your shell set-up.

Scratch files

One of the settings is the environment variable GAUSS_SCRDIR which is required to redirect the temporary files that Gaussian uses to the proper scratch space, presently

export GAUSS_SCRDIR=/global/scratch/hpcXXXX 

where hpcXXXX stands for your username. If for some reason Gaussian does not terminate normally (e.g. a job gets cancelled), it leaves behind large scratch files which you may have to delete manually. To check if such files exist, type

$ ls $GAUSS_SCRDIR
Gau-88477.chk  Gau-88477.int  Gau-88477.skr  
Gau-88477.d2e  Gau-88477.rwf  

Once you have determined that the scratch files are no longer needed (because the program that used them is not running any more), you can delete them by typing

$ rm $GAUSS_SCRDIR/Gau-*
$ ls $GAUSS_SCRDIR
$

Cleaning up the scratch space is the user's responsibility. If it is not done regularly, it can cause jobs to terminate, and much work to be lost.

Running Gaussian from a command line

To run Gaussian on our systems, you have to belong to a user group g98 (it's called that for historical reason, but it applies to all versions of Gaussian). You need to read our license agreement and signed a statement to be included in this user group. Once you are, you can access the executables.

A computation is performed by preparing an input file and pipe it to standard input of the program g16. Standard output should be caught in a log-file. We suggest you use the extensions .g16 for input files and .log for results.

Interactively, the command line to invoke Gaussian is thus:

 g16 < test.g16 >test.gout 

This will only work if you are a member of the g98 group and have set the environment correctly. Note that the interactive execution of Gaussian is only meant for test runs.

Gaussian input files are explained in the "User's Reference". It is impossible to give an outline here. Here is a small sample input file for test purposes:

%mem=512MB
#B3LYP/6-31G* opt

Test calculation

0 1
H1
O2 H1 R
H3 O2 R H1 A

R 1.1
A 107.

Important: Since Gaussian has recently moved from Solaris to Linux, the above command will work only on the Linux login node swlogin1, not (as before) on the Solaris-based sflogin0.

Note: It is absolutely essential to have a good idea about the size and complexity of your calculations before you start a Gaussian job. Many of the methods mentioned above have terrible scaling properties, i.e. the computational cost grows very quickly with the number of electrons, degrees of freedom, or number of basis functions used. We suggest you start with a small basis set and a cheap method, and then slowly increase those parameters.

Submitting (parallel) Gaussian jobs

If you want to run Gaussian on several processors on our machines, you have to include a line in your input file:

%nproc=8

where we assume that you want to use 8 processors (cores, threads).

It is mandatory to submit a Gaussian job script through our scheduling software.

On Frontenac

On Frontenac, you need to submit your Gaussian parallel production job through the SLURM scheduler (see our Scheduler Help File for details). This is done in the form of a script file. Here is a "bare bones" sample:

#!/bin/bash
#SBATCH --job-name=Gaussian_test
SBATCH --mail-type=ALL
#SBATCH --mail-user=myEmail@whatever.com
#SBATCH --output=STD.out
#SBATCH --error=STD.err
#SBATCH --nodes=1
#SBATCH --ntasks=1
#SBATCH --cpus-per-task=8
#SBATCH --time=30:00
#SBATCH --mem=1000
module load gaussian
export GAUSS_SCRDIR=$TMPDIR
g16 < test.g16 > test.log

• The "module" line makes sure the necessary setup is done.
• Email notifications are set up in the "--mail-type" and "--mail-user lines". We suggest "hpcXXXX@localhost" (hpcXXXX stands for the username). Place a file .forward containing your actual email address into your home directory.
• The --ooutput and --error lines are used to tell the system where to write "standard output" and "standard error", i.e. the screen output.
• The --ntasks and --nodes options are kept at 1 and indicate that only one main process is running on a single node.
• The --cpus-per-task line specifies the number of cores the scheduler will allocate (4 in this example). It is crucial to choose the same number as specified in the %nrocs= line of the input file.
• The "export" line resets the scratch space to a temporary directory that is created at run time. This ensures that left-over scratch files are erased if the program terminates.

The script (let's call it g16.sh) is submitted by the sbatch command:

sbatch g16.sh

Migration from SW cluster to Frontenac

The following is a list of differences concerning Gaussian usage on the SW cluster vs the new Frontenac cluster. The main impact comes from the different scheduler.

Licensing

Gaussian is a licensed program. The license held by the Centre for Advanced Computing is limited to our computers at our main site. That means that any of our users can use the program on our machines (but nowhere else), whether they are located at Queen's or not.

We require users of Gaussian to sign a statement in which they state that they are informed about the terms of the license to be included in the Gaussian user group named "g98". Please fax the completed statement to (613) 533-2015 or scan/email to cac.admin@queensu.ca.

Where can I get more detailed information ?

• To learn the basics about Gaussian input and output, refer to the Gaussian 16 User's Reference.
• For templates, and to get many examples, check out /opt/gaussian/g09/bsd/examples.
• The Gaussian web page contains a lot of information.
• For hardcore computational chemists, there is the Gaussian IOPs Reference, useful if you want to tinker with default settings and internal parameters.
• These can be purchased from Gaussian Inc..
• Send to cac.help@queensu.ca. We're happy to help.