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Fanpy is a free, open-source, and cross-platform Python 3 library designed for ab initio electronic structure calculations. The Fanpy implementation is based on the mathematical framework called Flexible Ansatz for N-electron Configuration Interaction (FANCI).
where
The FANCI ansatz offers a general wave-function structure that can be applied to various electronic structure theories, including Configuration Interaction (CI), Coupled-Cluster (CC), Tensor Product States (TPS), and Antisymmetrized Product of Interacting Geminals (APIG) wavefunctions.
Fanpy, a quantum chemistry code, offers tools to aid in developing novel electronic structure ansatz. Unlike other codes that provide well-established quantum methods and theories from the literature or recently developed by the group for a broader audience, Fanpy focuses on providing resources for researchers seeking to build new wavefunctions to solve chemical problems.
The FANCI framework provides a highly modular structure to Fanpy, resulting in five modules: Hamiltonian, Wavefunction, Objective, Solver, and Tools. This modular structure offers two significant advantages. Firstly, it enables a ‘sandbox-like’ approach to handling various combinations of wavefunction ansatz and different methods. Secondly, it simplifies the transition from the theoretical formulation of a method to its practical implementation.
For detailed information about the mathematical formulation, please take a look at the FANCI publication. The official notes of the Fanpy library can be found in this article.