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GNOCCHI

GNOCCHI is an in-house Python package to perform Generalised Normal-Ordered Coupled Cluster (GNOCC) calculations on spin eigenfunctions.

Currently, GNOCCHI is able to determine GNOCCSD (an analogue of CCSD for multi-reference systems) energies, obtain perturbative corrections, and even calculate some response properties. Additionally, it includes a module to construct configuration state functions (CSFs).

GNOCCHI is planned to be released in the near future.

Papers

  • Lee, Tew. Spin-free generalized normal ordered coupled cluster. J. Chem. Phys. 164, 134118 (2026) — spin-free, size-extensive, and numerically size-consistent coupled cluster method based on a generalized normal ordered exponential ansatz.