Fast and spectrally accurate construction of adaptive diagonal basis sets for electronic structure

TL;DR

This paper introduces a novel method combining periodic sinc basis sets with curvilinear coordinates, enabling faster, spectrally accurate electronic structure calculations with adaptive resolution and diagonal basis sets.

Contribution

It presents a new approach for constructing adaptive diagonal basis sets using pseudospectral methods and a novel coordinate transformation solving the Monge-Ampère equation.

Findings

Achieves faster convergence to the complete basis set limit.

Enables mean-field calculations with log-linear cost.

Ensures basis sets satisfy the diagonal approximation.

Abstract

In this article, we combine the periodic sinc basis set with a curvilinear coordinate system for electronic structure calculations. This extension allows for variable resolution across the computational domain, with higher resolution close to the nuclei and lower resolution in the inter-atomic regions. We address two key challenges that arise while using basis sets obtained by such a coordinate transformation. First, we use pseudospectral methods to evaluate the integrals needed to construct the Hamiltonian in this basis. Second, we demonstrate how to construct an appropriate coordinate transformation by solving the Monge-Amp\`ere equation using a new approach that we call the cyclic Knothe-Rosenblatt flow. The solution of both of these challenges enables mean-field calculations at a cost that is log-linear in the number of basis functions. We demonstrate that our method approaches the complete basis set limit faster than basis sets with uniform resolution. We also emphasize how these basis sets satisfy the diagonal approximation, which is shown to be a consequence of the pseudospectral method. The diagonal approximation is highly desirable for the solution of the electronic structure problem in many frameworks, including mean field theories, tensor network methods, quantum computing, and quantum Monte Carlo.