Q-Chem is a general purpose ab initio electronic structure program. Its latest version emphasizes Self-Consistent Field, especially Density Functional Theory, post Hartree-Fock, and innovative algorithms for fast performance and reduced scaling calculations. Geometry optimizations, vibrational frequencies, thermodynamic properties, and solution modeling are available. It performs reasonably well within its single reference paradigm on open shell and excited state systems. The Q-Chem Home Page has additional information.
Availability and Restrictions
Versions
Q-Chem is available on the OSC clusters. These are the versions currently available:
| Version | Pitzer | Ascend | Cardinal | Notes |
|---|---|---|---|---|
| 6.2.1 | X* | X | X | |
| 6.2.2 | X | X |
-mpi flag is required for running an MPI job, e.g., qchem -mpi -np 2. Without this flag, OpenMP will be used as the default parallelization method.module avail qchem to view available Q-Chem modules for a given machine.Access
Q-Chem is available to academic OSC users only. Please review the Q-Chem license agreement carefully before use. If you have any questions, please contact OSC Help.
Publisher/Vendor/Repository and License Type
Q-Chem, Inc., Commercial
Usage
For MPI jobs that request multiple nodes the job script must be run from a globally accessible working directory, e.g., project or home directories
Starting with version 5.1, QCSCRATCH is automatically set to $TMPDIR, which is removed once the job is completed. This setup helps conserve scratch space and improves job performance. If you need to save Q-Chem scratch files from a job for later use, set QCSCRATCH to a globally accessible working directory and QCLOCALSCR to $TMPDIR.
Usage
Set-up
Q-Chem usage is controlled via modules. Load one of the Q-Chem modulefiles at the command line, in your shell initialization script, or in your batch scripts. To load the default version of Q-Chem module, usemodule load qchem. To select a particular software version, use module load qchem/version
.Examples
- The root of the Q-Chem directory tree is $QC.
- Example Q-Chem input files are in the $QC/samples directory
Batch Usage
When you in login environment, you are actually logged into a linux box referred to as the login node. To gain access to the mutiple processors in the computing environment, you must submit your job to the batch system for execution. Batch jobs can request mutiple nodes/cores and compute time up to the limits of the OSC systems. Refer to Queues and Reservations and Batch Limit Rules for more info. Batch jobs run on the compute nodes of the system and not on the login node. It is desirable for big problems since more resources can be used.
Interactive Batch Session
For an interactive batch session one can run the following command:
salloc -A <project-account> -N 1 -n 1 -t 00:20:00
which requests one core (-N 1 -n 1), for a walltime of 20 minutes (-t 00:20:00). You may adjust the numbers per your need.
