An O(N^3) implementation of Hedin's GW approximation

TL;DR

This paper presents an efficient N^3 implementation of Hedin's GW approximation for molecules, utilizing localized functions and spectral methods to handle large organic systems more feasibly.

Contribution

The authors develop a novel N^3 scaling implementation of Hedin's GW approximation using localized functions and spectral methods for molecular systems.

Findings

Achieved N^3 computational complexity for GW calculations.

Implemented localized functions to describe correlation functions.

Utilized spectral functions for frequency dependence.

Abstract

Organic electronics is a rapidly developing technology. Typically, the molecules involved in organic electronics are made up of hundreds of atoms, prohibiting a theoretical description by wavefunction-based ab-initio methods. Density-functional and Green's function type of methods scale less steeply with the number of atoms. Therefore, they provide a suitable framework for the theory of such large systems. In this contribution, we describe an implementation, for molecules, of Hedin's GW approximation. The latter is the lowest order solution of a set of coupled integral equations for electronic Green's and vertex functions that was found by Lars Hedin half a century ago. Our implementation of Hedin's GW approximation has two distinctive features: i) it uses sets of localized functions to describe the spatial dependence of correlation functions, and ii) it uses spectral functions to treat their frequency dependence. Using these features, we were able to achieve a favorable computational complexity of this approximation. In our implementation, the number of operations grows as N^3 with the number of atoms N.