ORCA [CIT Research Documentation]

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====== ORCA ======

===== Accessing ORCA =====

The ORCA software is available on Habrok, but due to license reasons we have to ask every user to register for an ORCA license on the ORCA website first. You can do this on the following page:

https://orcaforum.kofo.mpg.de/ucp.php?mode=register

Once you've filled in this form, please forward the email confirmation that you will get to [[hpc@rug.nl]], and we can add you to the group of ORCA users and give you access to the software.
===== Using ORCA =====

The following example can be used as a job script for running ORCA jobs:

<code bash orca_example_job.sh>
#!/bin/bash
#SBATCH --job-name=orca
#SBATCH --time=0-24:00:00
#SBATCH --partition=regular
#SBATCH --ntasks=12
#SBATCH --cpus-per-task=1
#SBATCH --mem-per-cpu=1gb

module load ORCA/6.1.1-gompi-2023b-avx2
$EBROOTORCA/bin/orca my_orca_file.inp
</code>
This job scripts requests a total of 12x1 cores. It does not specify whether/how many tasks should be run on the same node: this can be achieved by using additional options like ''%%--ntasks-per-node%%'' and ''%%--nodes%%'', if necessary.

Note that ORCA itself will handle the parallelization by calling ''mpirun'', so you do not need to use ''mpirun'' or ''srun'' in your job script. You do have to call the ''orca'' executable with the full pathname, which you can easily do by using ''$EBROOTORCA'' (a variable that points to the ORCA installation directory).

Finally, make sure to use the same number of requested cores in your ORCA input file, e.g.:

<code txt my_orca_file.inp>
 %pal nprocs 12 end
 ! RHF TightSCF PModel
 !opt

 * xyz 0 1
  C 0.000000 0.000000 0.000000
  C 0.000000 0.000000 1.400000
  C 1.212436 0.000000 2.100000
  C 2.424871 0.000000 1.400000
  C 2.424871 0.000000 0.000000
  C 1.212436 0.000000 -0.700000
  H -0.943102 0.000000 1.944500
  H 1.212436 0.000000 3.189000
  H 3.367973 0.000000 1.944500
  H 3.367973 0.000000 -0.544500
  H 1.212436 0.000000 -1.789000
  H -0.943102 0.000000 -0.544500
 *

</code>