PSI4

Psi4 is an open-source quantum chemistry software project providing tools for computational chemistry in education, research, and industry. Its software combines a C++ and Python core with a flexible Python driver, allowing users to run calculations through straightforward input files and developers to integrate Psi4 into Python workflows or extend it with plugins and community projects.

The program supports methods including density functional theory (DFT), second-order Møller–Plesset perturbation theory (MP2), symmetry-adapted perturbation theory (SAPT), and coupled-cluster calculations. It uses techniques such as density fitting and is optimized for multicore execution. Psi4 also automates common tasks, including basis-set extrapolation and counterpoise correction, and offers documentation, tutorials, programming resources, and educational materials.

Distributed under the LGPL3 license, Psi4 is free to use and developed with attention to robustness, including continuous integration, code coverage checks, and regularly maintained documentation. Its broader software ecosystem includes standalone community projects and Psi4NumPy tutorials. The project also provides downloads, release information, publications, and a developer forum, supporting both practical use and continued development.