ORCA

Introduction

ORCA is a flexible, efficient and easy-to-use general purpose tool for quantum chemistry with specific emphasis on spectroscopic properties of open-shell molecules. It features a wide variety of standard quantum chemical methods ranging from semiempirical methods to DFT to single- and multireference correlated ab initio methods. It can also treat environmental and relativistic effects.

Licensing

If you wish to use pre-built ORCA executables at Cedar or Graham:

1. You have to register at https://cec.mpg.de/orcadownload/
2. Contact us requesting access to ORCA with a copy of the registration email

Using the software

ORCA 4.0.0.2 and 4.0.1.2 are installed on Cedar and Graham clusters. For detailed information about a specific "orca" module (including how to load the modules) use the module's full name. For example:

$ module spider orca/4.0.1.2

Job Submission

Cedar and Graham uses the Slurm scheduler; for details about submitting jobs, see Running jobs.

The following is a job script to run ORCA mpi job, run_orca.sh:

File : run_orca.sh

#!/bin/bash
 #SBATCH --ntasks=8                 # cpus, the nprocs defined in the input file
 #SBATCH --mem-per-cpu=3G           # memory per cpu
 #SBATCH --time=00-03:00            # time (DD-HH:MM)
 #SBATCH --output=benzene.log       # output .log file

module load openmpi/2.0.2
 module load orca/4.0.1.2
 $EBROOTORCA/orca benzen.inp

Example of the input file, benzene.inp:

File : benzen.inp

# Benzene RHF Opt Calculation
%pal nprocs 8 end
! RHF TightSCF PModel
! opt

* xyz 0 1
     C    0.000000000000     1.398696930758     0.000000000000
     C    0.000000000000    -1.398696930758     0.000000000000
     C    1.211265339156     0.699329968382     0.000000000000
     C    1.211265339156    -0.699329968382     0.000000000000
     C   -1.211265339156     0.699329968382     0.000000000000
     C   -1.211265339156    -0.699329968382     0.000000000000
     H    0.000000000000     2.491406946734     0.000000000000
     H    0.000000000000    -2.491406946734     0.000000000000
     H    2.157597486829     1.245660462400     0.000000000000
     H    2.157597486829    -1.245660462400     0.000000000000
     H   -2.157597486829     1.245660462400     0.000000000000
     H   -2.157597486829    -1.245660462400     0.000000000000
*

Example

Example results for benzene can be found on Graham under

/home/jemmyhu/tests/test_ORCA/