ORCA is a computational chemistry code that can do SCF, (TD)DFT, semi-empirical potentials, MP2, CASSCF, Coupled Cluster calculations, and more.
It is closed source, but free for academic users. Register on the forum to receive a download link for the binaries, as well as access ot the latest manual.
Many input examples are available at the ORCA Input Library.
ORCA ASE-interface is very simple. Two keywords are defined:
orcasimpleinput: str What you'd put after the "!" in an orca input file. orcablock: str What you'd put in the "% ... end"-blocks.
Setup and usage¶
The default command that ASE will use to start ORCA is
orca PREFIX.inp > PREFIX.out.
You can change this command by setting the
$ASE_ORCA_COMMAND. (For example, add a line
export ASE_ORCA_COMMAND="my new command").
This can be useful since the parallel MPI version of orca can require the full
path to the executable to be specified.
Orca wants to decide which sub-processes to parallelize via MPI itself, so you’d
almost always want a string in your
orcablocks specifying the number of
cores for the simulation, e.g.:
from ase.calculators.orca import ORCA calc = ORCA(label='orcacalc', orcasimpleinput='B3LYP def2-TZVP' orcablocks='%pal nprocs 16 end'
for a B3LYP/def2-TZVP calculation on 16 cores.