Subsystem-Based GW/Bethe–Salpeter Equation

Abstract

Subsystem Density-Functional Theory and its extension to excited states, namely, subsystem Time-Dependent Density-Functional Theory, have been proven to be efficient and accurate fragmentation approaches for ground and excited states. In the present study we extend this approach to the subsystem-based description of total systems by means of GW and the Bethe–Salpeter equation (BSE). For this, we derive the working equations starting from a subsystem-based partitioning of the screened-Coulomb interaction for an arbitrary number of subsystems. Making use of certain approximations, we develop a parameter-free approach in which environmental screening contributions are effectively included for each subsystem. We demonstrate the applicability of these approximations by comparing quasi-particle energies and excitation energies from subsystem-based GW/BSE calculations to the supermolecular reference. Furthermore, we demonstrate the computational efficiency and the usefulness of this method for the description of photoinduced processes in complex chemical environments.

The Seamless Connection of Local and Collective Excited States in Subsystem Time-Dependent Density Functional Theory

“…Alternatively, many-body perturbation techniques such as the GW/Bethe–Salpeter equation (BSE) could be used which offer a more favorable computation scaling than wave function-based methods. GW/BSE has been of increasing interest in the molecular electronic structure community in recent years, , and we have recently presented a subsystem-based derivation . The high quality of GW/BSE results for chlorophyll and bacteriochlorophyll molecules makes this method ideally suited for many biological systems in the context of photosynthesis.…”

Universal polarization energies for defects in monolayer, surface, and bulk hexagonal boron nitride: A finite-size fragments GW approach

“…If the fragments are identical, just translations of the same cluster with identical susceptibility blocks, calculating the overall χ 0 is independent of the system size. Such a fragment GW approach was used in particular in the study of π-conjugated organic crystals, with weak interactions between molecular units, [61,62] nanotube bundles [63] or layered 2D systems bound by weak van der Walls interactions, defining the field of 2D-genomics [64][65][66][67]. Further, such a partitioning of the independent-electron susceptibility served as the basis for combining the GW and Bethe-Salpeter [68][69][70] formalisms with semi-empirical continuous or discrete models of polarizable environments [71][72][73][74][75].…”

“…Such an approximation was shown to yield significantly too large gaps [77] but has been central to most studies implementing the fragment many-body techniques [62,81] or the combination of manybody techniques with models of dielectric environment [73,74]. In such studies, environmental corrections are calculated within the static COHSEX approximation in the form of a difference, namely that of the static COHSEX values of an energy level with and without the environment.…”

Fragment-Based Excited-State Calculations Using the GW Approximation and the Bethe–Salpeter Equation

“…9,30,31 A similar idea was independently proposed by Xuan et al their implementation is based on the plain-wave GW formulation in combination with the fragmentation of irreducible polarizability, referred to as "ADD-CHI approximation" in their manuscript. Recently, Tolle et al 33 have developed the subsystem-based GW/BSE method. Herein, we present the GW and GW/BSE implementations within the FMO method.…”

“…Along this line, we have developed a large-scale GW approach based on the fragment molecular orbital (FMO) method, which adopts the fragmentation approximation of irreducible polarizability. ,, A similar idea was independently proposed by Xuan et al; their implementation is based on the plain-wave GW formulation in combination with the fragmentation of irreducible polarizability, referred to as “ADD-CHI approximation” in their manuscript. Recently, Tölle et al have developed the subsystem-based GW/BSE method.…”