ORCA

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 to 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#

Orca can be configured using the configfile like other calculators. If you need to override it for programmatic control of the orca command, you can manually create an OrcaProfile:

from ase.calculators.orca import OrcaProfile

profile = OrcaProfile(command='/full/path/to/my/orca')
calc = ORCA(profile=profile)

ORCA decides which sub-processes to parallelize via MPI by itself, so you’ll 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(profile=MyOrcaProfile,
            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(*, profile=None, directory='.', **kwargs)[source]#

Class for doing ORCA calculations.

Example

calc = ORCA(charge=0, mult=1, orcasimpleinput=’B3LYP def2-TZVP’,

orcablocks=’%pal nprocs 16 end’)

Construct ORCA-calculator object.

Parameters:

  • charge (int)

  • mult (int)

  • orcasimpleinput (str)

  • orcablocks (str)

Examples

Use default values:

>>> from ase.calculators.orca import ORCA
>>> h = Atoms(
...     'H',
...     calculator=ORCA(
...         charge=0,
...         mult=1,
...         directory='water',
...         orcasimpleinput='B3LYP def2-TZVP',
...         orcablocks='%pal nprocs 16 end'))
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