Enhancements to the GW space-time method

TL;DR

This paper introduces enhancements to the real-space imaginary-time GW method, improving efficiency and accuracy for calculating self-energies in solids, enabling studies of larger and more complex systems.

Contribution

The paper presents novel techniques for tail fitting and band sum convergence acceleration in the GW scheme, expanding its applicability to larger systems.

Findings

Improved tail modeling reduces computational errors.

Accelerated band sum convergence decreases calculation time.

Enables analysis of surfaces, clusters, and defects.

Abstract

We describe the following new features which significantly enhance the power of the recently developed real-space imaginary-time GW scheme (Rieger et al., Comp. Phys. Commun. 117, 211 (1999)) for the calculation of self-energies and related quantities of solids: (i) to fit the smoothly decaying time/energy tails of the dynamically screened Coulomb interaction and other quantities to model functions, treating only the remaining time/energy region close to zero numerically and performing the Fourier transformation from time to energy and vice versa by a combination of analytic integration of the tails and Gauss-Legendre quadrature of the remaining part and (ii) to accelerate the convergence of the band sum in the calculation of the Green's function by replacing higher unoccupied eigenstates by free electron states (plane waves). These improvements make the calculation of larger systems (surfaces, clusters, defects etc.) accessible.