ORCA 2016

Introduction

The program ORCA is a modern electronic structure program package written by F. Neese, with contributions from many current and former coworkers and several collaborating groups. The binaries of ORCA are available free of charge for academic users for a variety of platforms. ORCA is a flexible, efficient and easy-to-use general purpose tool for quantum chemistry with specific emphasis on spectroscopic properties of open-shell molecules. It features a wide variety of standard quantum chemical methods ranging from semiempirical methods to DFT to single- and multireference correlated ab initio methods. It can also treat environmental and relativistic effects. Due to the user-friendly style, ORCA is considered to be a helpful tool not only for computational chemists, but also for chemists, physicists and biologists that are interested in developing the full information content of their experimental data with help of calculations. ORCA is able to carry out geometry optimizations and to predict a large number of spectroscopic parameters at different levels of theory. Besides the use of Hartee Fock theory, density functional theory (DFT) and semiempirical methods, high level ab initio quantum chemical methods, based on the configuration interaction and coupled cluster methods, are included into ORCA to an increasing degree.

Installed version

The currently installed versions of ORCA are 3.0.3 and 4.0.0:

$ module av ORCA

------------------------ /cm/shared/uniol/modules/chem -------------------------
   ORCA/3.0.3    ORCA/4.0.0 (D)
  Where:
   D:  Default Module

Using ORCA on the HPC cluster

You have to prepare a jobscript and an inputfile for your ORCA job. An example ORCA-job could look like this:

#SBATCH --partition=carl.p
#SBATCH --time=1-00:00:00
#SBATCH --mem=2G 
#SBATCH --job-name ORCA-TEST
#SBATCH --output=slurm-%j.out
#SBATCH --error=slurm-%j.err 
module load ORCA
MODEL=TiF3
ORCAEXE=`which orca`
$ORCAEXE ${MODEL}.inp > ${MODEL}.out

The first 5 lines are meant for SLURM. In the first line configuring the time needed for the job. Please be as accurate as possible but keep in mind that the job will fail if, e.g. the time is set to 1 hour but the job actually needs 5 hours. Second line defines the memory. For this job 2G (2Gb) should be enough. After that, we need to name our job, our example job is named "ORCA-TEST". The following two lines are defining the output- and the errorfile. Without adding these two lines, the output and errors will be saved into a single file.

Documentation

The full documentation of ORCA can be found here (PDF viewer required).