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

ORCA requires a license per individual or research group (cf. the ORCA forum). Once you can proof that you are eligible, contact for activation of the ORCA module.

Availability / Target HPC systems#

  • throughput cluster Woody and TinyFat
  • owing to its limited scalability, ORCA is not suited for the parallel computers

New versions of ORCA are installed by RRZE upon request with low priority if the users provide the installation files.


  • orca has to be called with the full path otherwise parallel runs may fail.
  • The orca module (module avail orca) will take care of loading an appropriate openmpi module, too.
  • ORCA often results in massive IO ("communication through files??"); thus, put temporary files into /dev/shm (RAM disk) or local scratch directory.

Sample job scripts#

parallel ORCA on a Woody node#

#!/bin/bash -l
#SBATCH --nodes=1 
#SBATCH --ntasks-per-node=4
#SBATCH --time=01:00:00
#SBATCH --export=NONE



module add orca/5.0.3

### No mpirun required as ORCA starts the parallel processes internally as needed. 
### The number of processes is specified in the input file using '%pal nprocs # end' 

${ORCABASE}/orca orca.inp "optional openmpi arguments"

Further information#

  • ORCA Forum
  • note in the ORCA forum on improving MKL performance on AMD EPYC processors: ORCA forum entry We recommend to not only set MKL_DEBUG_CPU_TYPE=5 but to also set MKL_CBWR=AUTO as environment variables (as long as ORCA still uses Intel MKL versions before 2020.1; these environment variables no longer work with newer MKL versions)