Flexible ansatz for N-body Configuration Interaction

TL;DR

The paper introduces FANCI, a versatile framework for constructing and optimizing a wide range of N-body wavefunctions, unifying various approaches like CI, Coupled-Cluster, and tensor networks.

Contribution

FANCI is a general framework that can reproduce and modify many wavefunction ansätze, enabling flexible exploration of new quantum chemistry methods.

Findings

Successfully reconstructs popular wavefunctions

Demonstrates the framework's flexibility and universality

Facilitates development of novel wavefunction forms

Abstract

We present a Flexible Ansatz for N-body Configuration Interaction (FANCI) that includes any multideterminant wavefunction. This ansatz is a generalization of the Configuration Interaction (CI) wavefunction, where the coefficients are replaced by a specified function of certain parameters. By making an appropriate choice for this function, we can reproduce popular wavefunction structures like CI, Coupled-Cluster, Tensor Network States, and geminal-product wavefunctions. The universality of this framework suggests a programming structure that allows for the easy construction and optimization of arbitrary wavefunctions. Here, we will discuss the structures of the FANCI framework and its implications for wavefunction properties, particularly accuracy, cost, and size-consistency. We demonstrate the flexibility of this framework by reconstructing popular wavefunction ans\"{a}tze and modifying them to construct novel wavefunction forms. FANCI provides a powerful framework for exploring, developing, and testing new wavefunction forms.