Q-Chem

Description

Q-Chem is a modern object-oriented quantum chemistry program. A variety of electronic structure methods (Hartree-Fock/SCF ,DFT, MPn, Coupled Cluster) are available. Q-Chem also includes a suite of tools for chemical and spectroscopic properties analysis.

Some of the methods in Q-Chem run only in serial mode - you cannot use these methods with more than one processor. Check the manual carefuly to see if the method you want to use can take advantage of more than one processor or not.

How to Access Q-Chem

NERSC uses modules to manage access to software.  To use the default version of Q-Chem, type:

%  module load qchem

Running Q-Chem on Franklin

Here is a sample batch script for Franklin:

#PBS -q debug 
#PBS -l mppwidth=4,walltime=00:30:00
#PBS -N qchem_test
#PBS -j oe
#PBS -V

module load qchem
cd $PBS_O_WORKDIR
qchem -np 4 infile outfile

Running multiple parallel qchem jobs simultaneously

If you have a few jobs that take similar time to complete, you may consider running them simultaneously.  Here is a sample job script that does this.  Please pay careful attention to the note below.

#PBS -q debug
#PBS -l mppwidth=32,walltime=00:30:00
#PBS -N qchem_test
#PBS -j oe
#PBS -V

module load qchem
cd $PBS_O_WORKDIR

qchem -np 8 infile1 outfile1 &
qchem -np 8 infile2 outfile2 &
qchem -np 8 infile3 outfile3 &
qchem -np 8 infile4 outfile4 

wait

Note: The "wait" command here is very important for all your jobs to complete normally. It ensures that the batch system will wait until all four qchem jobs finish. If it is missing at the end of the job script above (this is a common user error), then only the last job (that will not run in the background) will complete normally and there is no gurantee for the other three jobs. If the "wait" command is missing at the end of the job script, and the last job is also sent to the background (by having a "&" at the end of the last qchem -np line), the job will exit right after it starts, and may leave an orphaned reservation in the system. so you should avoid this error when running multiple qchem jobs.

Running Q-Chem on Carver

To run qchem parallel jobs interactively on Carver, you need to request a batch session using qsub -I command.

% qsub -I -V -l nodes=1:ppn=8 -q debug

And when the batch session is retured to you, type,

% cd $PBS_O_WORKDIR
% module load qchem
% qchem -np 8 infile outfile

To run batch jobs, you need to submit a batch script using the qsub command. Here is a sample batch script for Carver:

#PBS -S /bin/tcsh
#PBS -l nodes=1:ppn=8,walltime=2:00:00
#PBS -N qchem_test 
#PBS -j oe 
#PBS -q regular 
#PBS -V

cd $PBS_O_WORKDIR
module load qchem

qchem -np 8 infile outfile

Documentation

Q-Chem 3.1 Manual (PDF)

Q-Chem 3.2 Manual (PDF)

Availibility