ORCA

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.

The ORCA home page is at https://orcaforum.kofo.mpg.de

Licensing requirements

ORCA is released as precompiled binaries at no cost, pursuant to a closed-source licence.  Users are advised that the terms of the ORCA licence allow its use in the course of academic research only, and that each research group is expected to register with the ORCA developers. If you have any questions regarding your eligibility to access ORCA or any particular version of it, please contact our support desk.

Example script

#!/bin/bash -e
#SBATCH --job-name      ORCA_job
#SBATCH --time          01:00:00
#SBATCH --ntasks        16  # ORCA can be inefficient with ntasks > 16
#SBATCH --mem-per-cpu   1G

module load ORCA/4.2.1-OpenMPI-3.1.4

# ORCA under MPI requires that it be called via its full absolute path orca_exe=$(which orca) # Don't use "srun" as ORCA does that itself when launching its MPI process. ${orca_exe} MyInput.inp

Further notes

Requesting a parallel run

ORCA requires a parallel run to be requested in its input as well as from the batch scheduler. To request a parallel run, you need to add a line to the input file like the following:

%pal nprocs <np> end

where <np> represents the total number of processors (cores) you have requested from the scheduler.

Checkpointing and restarting

ORCA provides for saving of checkpoint data, especially molecular orbital information, in a file with extension ".gbw" (short for Geometry-Basis-Wavefunction). Given an input file name of "foo.inp" or some equivalent, the GBW file will be named "foo.gbw". The GBW file, like temporary and other output files, will be written in the same directory from which the ORCA executable is invoked.

To restart from an existing GBW file, you should do the following:

  1. Ensure that the GBW file you want to start from is renamed so that it does not have the same base name as your intended input file. Otherwise, it will be overwritten and destroyed as soon as ORCA starts running.
  2. In your input file, specify the following lines, replacing "checkpoint.gbw" with the name of the GBW file you intend to read from:
! moread
% moinp "checkpoint.gbw"
  1. Run the calculation.

For more information about restarting from an older GBW file, including how to restart from GBW files produced using earlier versions of ORCA, please consult the ORCA manual.

Labels: mahuika tier1 chemistry
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