ORCA

Set-up

ORCA usage is controlled via modules. Load one of the ORCA modulefiles at the command line, in your shell initialization script, or in your batch scripts. To load the default version of ORCA module, use module load orca. To select a particular software version, use module load orca/{version}. For example, use module load orca/4.2.1to load ORCA version 4.2.1.

Batch Usage

When you log into pitzer.osc.edu or pitzer.osc.edu, you are actually logged into a linux box referred to as the login node. To gain access to the mutiple processors in the computing environment, you must submit your job to the batch system for execution. Batch jobs can request mutiple nodes/cores and compute time up to the limits of the OSC systems. Refer to Queues and Reservations and Batch Limit Rules for more info.  Batch jobs run on the compute nodes of the system and not on the login node. It is desirable for big problems since more resources can be used.

Interactive Batch Session

For an interactive batch session one can run the following command:

sinteractive -A <project-account> -n 1 -t 00:20:00

which requests one core (-n 1), for a walltime of 20 minutes (-t 00:20:00). You may adjust the numbers per your need.

Non-interactive Batch Job

A batch script can be created and submitted for a serial or parallel run. You can create the batch script using any text editor you like in a working directory on the system of your choice. Below is the example batch script for a parallel run:

#!/bin/bash
#SBATCH --job-name=orca_mpi_test
#SBATCH --time=0:10:0
#SBATCH --nodes=2 --ntasks-per-node=<number-of-cores-per-node>
#SBATCH --account=<project-account>

module reset
module load openmpi/3.1.6-hpcx
module load orca/4.2.1
module list

sbcast -p h2o_b3lyp_mpi.inp $TMPDIR/h2o_b3lyp_mpi.inp
cd $TMPDIR
$ORCA/orca h2o_b3lyp_mpi.inp > $SLURM_SUBMIT_DIR/h2o_b3lyp_mpi.out

Please note that the <number-of-cores-per-node> cannot exceed the maximum cores per node. You can refer to Cluster Computing for the maximum number for each cluster.

Set correct value for %maxcore

In general, it is recommended to utilize 3000, which is 75% of the usable memory per core on each cluster. However, you may need to increase %maxcore due to the methods and the modular system. In this case, you can decrease the number of cores for the same job. For example, if you have the following script to run an 80-core ORCA job on two Pitzer 40-core nodes:

#!/bin/bash
#SBATCH --nodes=2 --ntasks-per-node=40

module reset
module load openmpi/3.1.6-hpcx
module load orca/4.2.1
module list

sbcast -p h2o_b3lyp_mpi.inp $TMPDIR/h2o_b3lyp_mpi.inp
cd $TMPDIR
$ORCA/orca h2o_b3lyp_mpi.inp > $SLURM_SUBMIT_DIR/h2o_b3lyp_mpi.out

If you need to increase %maxcore to 4000, you can run ORCA with 60 cores (30 cores per node) in the same job script by replacing the ORCA command line with:

$ORCA/orca h2o_b3lyp_mpi.inp "--npernode=30" > $SLURM_SUBMIT_DIR/h2o_b3lyp_mpi.out