psiCI: a configuration-interaction module using Psi4 with DFT/HF orbitals

Use psiCI to perform configuration-interaction (CI) calculations with Psi4 using density-functional theory (DFT) and Hartree-Fock (HF) orbitals. The module enable CI calculations using arbitrary configuration space for the CI expansion. It also provides support for building the configuration space associated with common active space (single- and multi-reference CIS(DT) and CAS/RAS). psiCI is a Python class.

Dependencies: psiCI requires the numpy, scipy, itertools, and psi4 packages.

Content

Root folder in main:

• psiCI.py is the CI module itself
• documentation.ipynb is the documentation for the module, including a description of the methods, input parameters, and output as well as a few examples
• test_PsiCI.ipynb can be used to test the CI module (for future updates)

Examples folder:

• Configuration_basis.ipynb illustrates CI calculations with various sets of molecular orbitals (HF vs DFT)
• H2O_molecule.ipynb illustrates CI calculations in the H₂O molecule (with a 3500 configuration state basis)

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Reference

• G. Visentin and F. Mauger, Configuration-interaction calculations with density-functional theory molecular orbitals for modeling valence- and core-excited states in molecules, arXiv:2509.08245 (2025)

@article{Visentin2025,
  title = {Configuration-interaction calculations with density-functional theory molecular orbitals for modeling valence- and core-excited states in molecules},
  author = {Visentin, Giorgio and Mauger, Fran\c{c}ois},
  journal = {arXiv:2509.08245},
  year = {2025}
}

For more information: [email protected]

Acknowledgments

The development and implementation of psiCI was supported by the National Science Foundation under Grant No. PHY-2207656.

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