# psi4/psi4

Open-Source Quantum Chemistry – an electronic structure package in C++ driven by Python

Repository: https://github.com/psi4/psi4
Canonical: https://ross.abutalabs.com/products/psi4
Homepage: http://psicode.org
Language: C++
License: LGPL-3.0
License Family: copyleft
Topics: quantum-chemistry, c-plus-plus, python, computational-chemistry, chemistry, physics
Last push: 2026-08-26T04:02:48+00:00

## Health v2 (maintenance only)
Score: 96/100 (v2, computed 2026-09-02T17:46:02.011165+00:00)
- activity 99, release rhythm 90, longevity 100
- inputs: {"age_days": 4901, "days_push": 7, "days_rel": 64, "gap_med": 15, "n_releases_24m": 4}
- flags: none
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 1215, forks 510 (observed 2026-08-28T04:04:01.080649+00:00)

## What it is
Psi4 is an open-source quantum chemistry package for electronic structure calculations, with computationally demanding code in C++ and a flexible Python driver. It supports methods from Hartree-Fock and DFT to coupled cluster, SAPT, and multireference theory, usable both as an executable and as a Python module.

## Use cases
- compute molecular energies and geometries with DFT or coupled cluster
- run quantum chemistry calculations from Python scripts
- perform symmetry-adapted perturbation theory (SAPT) on molecular complexes
- optimize molecular geometries and compute vibrational frequencies
- teach computational chemistry in university labs
- calculate intermolecular interaction energies with counterpoise correction

## When to choose
- you need a free, open-source electronic structure package with modern methods like DLPNO-CCSD(T) and F12
- you want to script quantum chemistry workflows via a Python API or QCSchema
- you need fast multicore execution of DFT, MP2, SAPT, or coupled-cluster calculations
- you want an extensible platform that integrates with the QCArchive ecosystem

## When to avoid
- you need a graphical molecular builder or visualization frontend
- you require methods outside Psi4's supported set or highly specialized proprietary codes
- you want a lightweight tool for quick back-of-the-envelope chemistry without HPC resources

## Facets
- artifact type: application
- maturity: active
- function: simulation, sdk, cli, developer-tools
- domain: chemistry, data-science, education
- platform: windows, python, cpp, cli
- tags: quantum-chemistry, electronic-structure, computational-chemistry, dft, coupled-cluster, sapt, molecular-modeling, scientific-computing, physics, linux, macos

## Member repositories
- psi4/psi4 (main) score 96

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:04:01.080649+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-30T06:17:17.803699+00:00, confidence not recorded.
  - readme: https://github.com/psi4/psi4 (fetched 2026-08-28T04:04:01.080649+00:00, sha fdb8b2f8294a)
  - homepage: http://psicode.org (fetched 2026-08-29T12:25:20.159918+00:00, sha 878f2c8f40c0)
  - site_page: https://psicode.org/installs/latest (fetched 2026-08-29T12:25:20.170840+00:00, sha 36597ec3a0dd)
  - site_page: https://psicode.org/categories/releases (fetched 2026-08-29T12:25:20.174176+00:00, sha d4aef5474d40)
  - site_page: https://psicode.org/psi4manual/master/index.html (fetched 2026-08-29T12:25:20.168889+00:00, sha b14852bad798)
- Data as of 2026-08-30T08:39:29.467469+00:00.