Bethe Salpeter Equation Spectra for Very Large Systems

Abstract

We present a highly efficient method for the extraction of optical properties of very large molecules via the Bethe-Salpeter equation. The crutch of this approach is the calculation of the action of the effective Coulombic interaction, W , through a stochastic TD Hartree propagation, which uses only 10 stochastic orbitals rather than propagating the full sea of occupied states. This leads to a scaling that is at most cubic in system size, with trivial parallelization of the calculation. We apply this new method to calculate the spectra and electronic density of the dominant excitons of a carbonnanohoop bound fullerene system with 520 electrons, using less than 4000 core hours.

Connecting the dots for fundamental understanding of structure–photophysics–property relationships of COFs, MOFs, and perovskites using a Multiparticle Holstein Formalism

“…Despite significant recent progress, two main challenges still persist which involve a quantitative understanding of how electron-phonon coupling and defects influence the electronic, optical, and transport properties of functional electronic materials. Although, excited state properties of materials can be modeled using linear-response time-dependent density functional theory (LR-TDDFT) or the Bethe-Salpeter equation (BSE), 164 the presence of a large number of atoms in 2D materials makes the application of LR-TDDFT and BSE computationally very demanding (however, recent advances do look very promising 165,166 ). Moreover, electron-phonon coupling and different forms of electronic and conformational defects play fundamental roles in determining the photophysical response and, consequently, the transport properties of most organic and hybrid materials.…”

Gapped-filtering for efficient Chebyshev expansion of the density projection operator

“…These polynomial expansions are also the primary ingredient in stochastic quantum chemistry methods, [4] including stochastic DFT [5][6][7] and beyond-DFT approaches. The latter include the linear-scaling stochastic-GW method (sGW) [8] which calculates the quasiparticle (QP) energy as a perturbative correction to the DFT eigenvalue [9][10][11][12], as well as, e.g., stochastic-MP2 [13] stochastic Bethe Salpeter Equation [14] and stochastic Time-Dependent DFT (TDDFT) [15].…”