Structure Optimization with Stochastic Density Functional Theory

TL;DR

This paper introduces a stochastic structure optimization method within stochastic density functional theory (sDFT), combining noise-reduction and stochastic optimization algorithms to efficiently determine ground state structures of extended systems.

Contribution

It develops and compares stochastic gradient-based and Hessian-based optimization algorithms tailored for sDFT, improving structure optimization efficiency.

Findings

Stochastic gradient descent methods outperform Hessian-based methods in efficiency.

Noise-reduction schemes significantly improve the stability of sDFT-based optimization.

Performance depends on optimization parameters and system size.

Abstract

Linear-scaling techniques for Kohn-Sham density functional theory (KS-DFT) are essential to describe the ground state properties of extended systems. Still, these techniques often rely on the locality of the density matrix or on accurate embedding approaches, limiting their applicability. In contrast, stochastic density functional theory (sDFT) achieves linear- and sub-linear-scaling by statistically sampling the ground state density without relying on embedding or imposing localization. In return, ground state observables, such as the forces on the nuclei, fluctuate in sDFT, making the optimization of the nuclear structure a highly non-trivial problem. In this work, we combine the most recent noise-reduction schemes for sDFT with stochastic optimization algorithms to perform structure optimization within sDFT. We compare the performance of the stochastic gradient descent (sGD) approach and its variations (stochastic gradient descent with momentum (sGDM)) to stochastic optimization techniques that rely on the Hessian, such as the stochastic Broyden-Fletcher-Goldfarb-Shanno (sBFGS) algorithm. We further provide a detailed assessment of the computational efficiency and its dependence on the optimization parameters for each methods for determining the ground state structure of bulk silicon with varying supercell dimensions.