ORCA¶

What is ORCA?¶

ORCA is a quantum chemistry software package for electronic structure calculations. It supports DFT, coupled cluster, multireference methods, and spectroscopic property calculations.

Important

ORCA does NOT support GPU acceleration and does not utilize GPUs.

The ORCA module is not available on GPU nodes.

Use the CPU partition for all ORCA calculations.

Base Environment

ORCA is provided via the environment modules system.

Loading ORCA¶

Load module

module load orca/6.1.1

Best Practice

Always verify the loaded version:

module list

Example Input File¶

water.inp

DFT geometry optimization

! B3LYP def2-SVP Opt

* xyz 0 1
O   0.0000   0.0000   0.0000
H   0.7570   0.5860   0.0000
H  -0.7570   0.5860   0.0000
*

SLURM Job Script (Serial)¶

orca_job.sh

Serial ORCA job

#!/bin/bash
#SBATCH --job-name=orca_test
#SBATCH --partition=CPU
#SBATCH --nodes=1
#SBATCH --ntasks=1
#SBATCH --mem=8G
#SBATCH --time=01:00:00
#SBATCH --output=orca_%j.out

module load orca/6.1.1

orca water.inp > water.out

Submit job

sbatch orca_job.sh

Checking Job Completion¶

Successful termination

grep "ORCA TERMINATED NORMALLY" water.out

Expected output:

****ORCA TERMINATED NORMALLY****

Output Files¶

File	Description
`.out`	Main output with all results and calculation details
`.xyz`	Final optimized geometry (for Opt jobs)
`_trj.xyz`	Optimization trajectory
`.gbw`	Wavefunction data (required for restarts)

Parallel Execution¶

PAL setting

It is strongly recommended to set PAL equal to --ntasks.

Other configurations may lead to poor performance or job failure.

Input File (4 cores)¶

water.inp with PAL4

water.inp with PAL4

! B3LYP def2-SVP Opt
! PAL4

* xyz 0 1
O   0.0000   0.0000   0.0000
H   0.7570   0.5860   0.0000
H  -0.7570   0.5860   0.0000
*

SLURM Script (4 cores)¶

orca_job.sh

Parallel ORCA job

#!/bin/bash
#SBATCH --job-name=orca_parallel
#SBATCH --partition=CPU
#SBATCH --nodes=1
#SBATCH --ntasks=4
#SBATCH --mem=8G
#SBATCH --time=01:00:00
#SBATCH --output=orca_%j.out

module load openmpi/4.1.7
module load orca/6.1.1

$(which orca) water.inp > water.out

Submit

sbatch orca_job.sh

More Information¶

Documentation

Official ORCA manual:

https://www.faccts.de/docs/orca/6.1/manual/index.html