Large-scale GW -BSE calculations with N3 scaling: Excitonic effects in dye-sensitized solar cells

Abstract

Excitonic effects due to electron-hole coupling play a fundamental role in renormalising energy levels in dye sensitised and organic solar cells determining the driving force for electron extraction. We show that first-principles calculations based on many-body perturbation theory within the GW-BSE approach provide a quantitative picture of interfacial excited state energetics in organic dyesensitized TiO2, delivering a general rule for evaluating relevant energy levels.To perform GW-BSE calculations in such large systems we introduce a new scheme based on maximally localized Wannier's functions. With this method the overall scaling of GW-BSE calculations is reduced from O(N 4 ) to O(N 3 ).

Electronic structure and optical properties of isolated and TiO2‐grafted free base porphyrins for water oxidation: A challenging test case for DFT and TD‐DFT

“…Here, the picture is more complicated, with a differential response of the porphyrin and TiO 2 energy levels at the different functionals, translating into a completely altered interfacial energetics as the functional is changed. In this context, although computationally much more expensive, many body perturbation theory, that is, GW/BSE, calculations have been shown to lead to better agreement with experiments compared to the estimates obtained from the Kohn−Sham eigenvalue …”

“…In this context, although computationally much more expensive, many body perturbation theory, that is, GW/BSE, calculations have been shown to lead to better agreement with experiments compared to the estimates obtained from the Kohn −Sham eigenvalue. [97][98][99] Finally, when the rigorously calculated GSOP and ESOP values for the isolated molecule are concerned, M06-2X is the functional providing the better agreement with experiments (see data in Table 4), with deviations of 0.04/0.29 eV for GSOP/ESOP. Surprisingly, B3LYP, CAM-B3LYP, and ωB97X-D, despite their dramatically different electronic structure description, deliver similar results, significantly underestimating GSOP ($ 0.5 eV) and, consequently, ESOP (0.4-0.5 eV).…”

Giant excitonic absorption and emission in two-dimensional group-III nitrides

“…For the lowest-energy, at the onset of the absorption spectrum, ground-state bound excitons S = 0 , Q = 0 binding energy E b and radius r exc , obtained within the accurate, but computationally heavy BSE calculations 31 , are compared with predictions of an analytical model of excitons in two dimensions 32,33 . The model Schrödinger equation in (SM1) relies on the effective mass approximation (EMA), with the reduced exciton mass µ = m e m h /(m e + m h ) in terms of the electron (hole) mass m e ( m h ) extracted from the dispersion of the lowest conduction (highest valence) band.…”

Ab initio modeling of excitons: from perfect crystals to biomaterials

“…Recent developments [122,123] and increased computing power have allowed to treat larger systems, such as reconstructed surfaces, defect structures, or in general materials with more complex structures. Yet, studies of the exciton properties in some of the currently most intriguing systems are still extremely difficult to perform.…”