Q-Chem

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

• Setup
• Files and Disk Usage
• Examples
• Documentation and Help

Setup

The modules package controls access to Q-Chem software.

To use the default version of Q-Chem, load the module:

%  module load qchem

You can customize your Q-Chem environment by putting Q-Chem directives in a ~/.qchemrc file. Be careful not to put tabs in your .qchemrc. System wide defaults in (/usr/common/usg/qchem/{version}/config/preferences) take presidence over ~/.qchemrc preferences.

After the module is loaded you can run qchem using

% qchem -np #n infile outfile 

Where #n describes the total number of tasks you've chosen. Or, for serial jobs

% qchem infile outfile 

Files and Disk Usage

The envronment variable $QCSCRATCH defines the location of on disk scratch and other temporary output files. By defualt this is the same as $SCRATCH.

To save scratch files for restart in a subdirectory of $QCSCRATCH, you may specify the name of the subdirectory as a third argument on the command line. E.g.,

%  qchem infile outfile save_dir 

will save intermediate results to $QCSCRATCH/savedir. The files saved there may be used in conjuction with a READ directive to restart a calculation.

% qchem infile outfile save_dir 

Examples

Examples are in /usr/common/usg/qchem/{version}/samples.

The general syntax for running the examples is quite simple:

% qchem infile outfile

The output in outfile should conclude with the usage summary

 Total job wall time:  4.00E+05 s
 Total time  CPU 1.72E+05 s  wall 4.00E+5 s
 Total time: CPU: 1.72E+05 System: 4.50E+04 Wall: 4.00E+05

Documentation and Help

• Q-Chem 2.0 Manual (PDF)
• Q-Chem 3.0 Manual (PDF)