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ORCA

A flexible, efficient and easy-to-use general purpose tool for quantum chemistry with specific emphasis on spectroscopic properties.

Homepage Version(s): 5.0.1; 4.1.2

ORCA requires an environment module

In order to use ORCA, you must first load the appropriate environment module: 

module load gnu openmpi orca

ORCA is computational chemistry program focusing on quantum chemistry applications. The program is designed for modeling electronic structures as well as spectroscopic properties of molecules. The program contains a variety of different methods for performing such simulations.

Using ORCA on RCC Resources#

The ORCA quantum chemistry tool is available on the HPC cluster for parallel processing of ORCA jobs.

In order to use ORCA, you must load the gnu, openmpi, and orca modules:

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module load gnu openmpi orca

To load ORCA v4.1.2, you'll need to load the old OpenMPI v2.1.0 module:

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module load gnu openmpi/2.1.0 orca

Submitting a Job#

Following is a sample ORCA input parameter file. Note the line ! PAL``x (x = 2 in the example) at the beginning where x is the number of parallel processes you would like to run simultaneously.

MY-INPUT-FILE.inp:

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## My first parallel ORCA calculation :-)
#
! PAL2
! HF SVP
* xyz 0 1
C 0.0 0.0 0.0
O 0.0 0.0 1.13
*

Create a SLURM submission script. For example:

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#!/bin/bash
#SBATCH -t 00:10:00
#SBATCH -n 2
#SBATCH --ntasks-per-node=1
#SBATCH -A $SLURM_ACCOUNT
module load gnu openmpi orca
orca MY-INPUT-FILE.inp

Note that ORCA may throw an error relating to an inability to access or execute an executable file. If this occurs, then you will need to provide the entire absolute file path when calling ORCA. See the Troubleshooting section below for details.

Testing ORCA scripts#

You can also run ORCA scripts on the HPC login nodes for testing purposes only. Ensure that you remove the ! PAL``x line:

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module load gnu openmpi orca
orca MY-INPUT-FILE.inp

Unload the conflicting module first, for example, by running module purge before you load the ORCA module.

If ORCA throws an error relating to an inability to access or execute an executable file, the way to fix it, according to the ORCA Users Manual on the official website, is to type the entire path to ORCA on the HPC before the .inp file when calling the program. For example:

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$PATH MY-INPUT-FILE.inp

Where $PATH is the complete absolute file path which can be found using which orca. Once which orca is run, just copy and paste the absolute file path it returns into the command line or the line in your SLURM submission script that calls ORCA and type the input file's name as shown above.