ORCA Meets PythonThe ORCA Python Interface OPI

The ORCA program suite is one of the most widely used
quantum chemistry
software packages. It features a wide range of electronic structure
methods and algorithms for the prediction of molecular chemical properties,
reactivity, and spectroscopy. In this paper, we present a fully featured
ORCA Python Interface termed OPI to drastically increase the accessibility
of ORCA’s method portfolio and enable efficient automation
of quantum chemical workflows. OPI is an open-source Python library
that provides straightforward low-level access to ORCA’s input,
execution, and output with a few lines of Python code. In the following,
we introduce OPI version 2.0 and its key features, also outlining
its general architecture. In addition, we demonstrate its application
through several diverse examples of quantum chemical workflows. These
examples include a system-dependent optimal-tuning procedure for range-separated
hybrid functionals, generation of training data for machine learning
purposes, orbital localization and visualization for chemical education,
and calculations with density functional ensembles. Finally, we outline
the current status of OPI and future plans for its development. OPI
is compatible with ORCA ≥ 6.1.1 and Python ≥ 3.11. The
project, its code, and its including documentation are available at https://github.com/faccts/opi. OPI is also available through PyPI (https://pypi.org/project/orca-pi).