ORCA

ORCA is an ab initio quantum chemistry program package that contains modern electronic structure methods including density functional theory, many-body perturbation, coupled cluster, multireference methods, and semi-empirical quantum chemistry methods. Its main field of application is larger molecules, transition metal complexes, and their spectroscopic properties.[1][2][3]

Installed Version

ORCA 5.0.3 is installed. Use the modulefile:

orca/5.0.3

How to Run

N.B. despite using MPI, Orca seems to be able to run on a single-node only due to the non-standard way it uses MPI. See this article from the Ohio Supercomputing Center documentation.

Example

Input file below. Note the line “%PAL NPROCS 48 END” which specifies that Orca should run in parallel with 48 processes (i.e. MPI ranks). This is specified separately from the job script “--ntasks-per-node=48” and must match that value.

This is unlike normal MPI programs which can run on multiple nodes, and infer the process distribution from the Slurm resource request.

Example input file (named “geom.inp”)

!B3LYP DEF2-SVP OPT
%PAL NPROCS 48 END
* xyz 0 1
N         -0.83911        0.76325       -0.31843
C          0.61442        0.72014       -0.25075
C          1.01669       -0.56167        0.49740
O          0.20095       -1.36984        0.93753
H         -1.37884        0.05803        0.17605
H          1.00414        0.66192       -1.27362
C          1.17285        1.95192        0.45211
H          0.87124        2.87150       -0.05988
H          0.81191        2.01288        1.48492
H          2.26726        1.92903        0.48485
H         -1.30551        1.57618       -0.71069
O          2.33980       -0.77979        0.66176
H          3.04559       -0.08055        0.28096
*

Job script:

#!/bin/bash
#SBATCH --time=1:00:00
#SBATCH --nodes=1
#SBATCH --ntasks-per-node=48
#SBATCH --time=1:00:00
#SBATCH --mem-per-cpu=3G

module load orca

${ORCADIR}/bin/orca ./geom.inp

References

[1] :Wikipedia:ORCA (quantum chemistry program)

[2] Fast & Accurate Computational Chemistry Tools]

[3] ORCA Forum