ORCA¶
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.
The ORCA
ASE-interface is very simple. Two keywords are defined:
orcasimpleinput: str
What you'd put after the "!" in an orca input file.
orcablocks: str
What you'd put in the "% ... end"-blocks.
The ASE-calculator also works with the
EIQMMM
-calculator
for QM/MM simulations (see qmmm
for
more info).
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
environment variable $ASE_ORCA_COMMAND
. (For example, add a line
to your .bashrc
with 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.
Class Definition¶
- class ase.calculators.orca.ORCA(restart=None, ignore_bad_restart_file=<object object>, label='orca', atoms=None, **kwargs)[source]¶
ASE interface to ORCA 4 by Ragnar Bjornsson, Based on NWchem interface but simplified. Only supports energies and gradients (no dipole moments, orbital energies etc.) for now.
For more ORCA-keyword flexibility, method/xc/basis etc. keywords are not used. Instead, two keywords:
- orcasimpleinput: str
What you’d put after the “!” in an orca input file. Should in most cases contain “engrad” or method that writes the engrad file. If not (single point only), set the “task” parameter manually. Default is
engrad tightscf PBE def2-SVP
.- orcablocks: str
What you’d put in the “% … end”-blocks. Default is
%scf maxiter 200 end
.
are used to define the ORCA simple-inputline and the ORCA-block input. This allows for more flexible use of any ORCA method or keyword available in ORCA instead of hardcoding stuff.
Default parameters are:
charge: 0
mult: 1
task: ‘gradient’
Point Charge IO functionality added by A. Dohn.