Orbital-enriched Flat-top Partition of Unity Method for the Schr\"odinger Eigenproblem

TL;DR

This paper introduces a stable, efficient orbital-enriched partition-of-unity method for solving the Schrödinger eigenproblem, reducing computational complexity while maintaining accuracy through flat-top properties and variational lumping.

Contribution

It develops a novel flat-top partition-of-unity approach with orbital enrichment, addressing stability and efficiency issues in quantum mechanical eigenproblem solutions.

Findings

Achieves accurate solutions with fewer degrees of freedom.

Demonstrates improved stability and computational efficiency.

Ensures p-th order completeness with orthogonal polynomials.

Abstract

Quantum mechanical calculations require the repeated solution of a Schr\"odinger equation for the wavefunctions of the system. Recent work has shown that enriched finite element methods significantly reduce the degrees of freedom required to obtain accurate solutions. However, time to solution has been adversely affected by the need to solve a generalized eigenvalue problem and the ill-conditioning of associated systems matrices. In this work, we address both issues by proposing a stable and efficient orbital-enriched partition-of-unity method to solve the Schr\"odinger boundary-value problem in a parallelepiped unit cell subject to Bloch-periodic boundary conditions. In our proposed PUM, the three-dimensional domain is covered by overlapping patches, with a compactly-supported, non-negative weight function, that is identically equal to unity over some finite subset of its support associated with each patch. This so-called flat-top property provides a pathway to devise a stable approximation over the whole domain. On each patch, we use $p$-th degree orthogonal polynomials that ensure $p$-th order completeness, and in addition include eigenfunctions of the radial solution of the Schr\"odinger equation. Furthermore, we adopt a variational lumping approach to construct a block-diagonal overlap matrix that yields a standard eigenvalue problem and demonstrate accuracy, stability and efficiency of the method.