Tag Archives: Bethe-Salpeter

Direct and indirect excitons in boron nitride polymorphs: a story of atomic configurations and electronic correlation

In this work we study how different atomic configurations, and electronic correlation modify the exciton dispersion in hexagonal boron nitride. We use two different approaches, ab-initio DFT plus many-body perturbation theory and tight-binding. We found that in the case of AB-stacking electronic correlation inverts the nature of the optical gap, from indirect to direct respect… Read More

Speed up dielectric constant calculations using the double-grid method with Yambo

Convergence of dielectric constant with respect the number of k-points can be very slow in many systems. For this reason in Yambo it is implemented a double-grid technique that speeds up convergence versus k-points with a computational cost comparable to the standard calculations. The method is described in the paper: Speeding up the solution of… Read More

Exciton interference in hexagonal boron nitride

Our new paper on exciton interference in hexagonal boron nitride is online. In this paper we show  that the excitonic peak  at finite momentum is formed by the superposition of two groups of transitions that we call KM and MK′ from the k-points involved in the transitions. These two groups contribute to the peak intensity… Read More

Optical properties of extended systems within a current-current response formalism: tips and tricks

In this work we compare the optical absorption of extended systems calculated starting from the density-density and current-current linear response formalisms within the equilibrium many-body perturbation theory(MBPT). We show how, using the latter, one can incur in errors due to quasiparticle lifetimes, electron-hole interaction or the presence of a Drude tail. These errors are found… Read More

Reasonable parameters for Yambo calculations

Here I report some advices to choose reasonable parameters in order to converge different kind of calculations with the Yambo code. The following parameters are a reasonable recommendation. However you have to remember that convergence can be different from system to system, so you should check your calculations and not use the following parameters blindly…. Read More

Nonlinear response of solids within the GW plus Bethe-Salpeter approximation

My new talk for the GDR-Corr is available online. In this talk I will present our new (probably not so new now) approach to calculate non-linear response in extended systems within the GW plus Bethe-Salpeter equation. I  put different references in the presentation that can be interesting for the reader.

Optical properties of Cu-chalcogenide photovoltaic absorbers from self-consistent GW and the Bethe-Salpeter equation

We pubblised a new paper1 on the optical properties of Cu-chalcogenide photovoltaic absorbers. In this manuscript we  calculate the optical response of the less studied, but promising, Cu2ZnGe(S,Se)4 compounds, opening the way to predictive calculations of still unknown materials by means of self-consistent GW plus Bethe-Salpeter equations. Moreover in this paper we solved the problem… Read More

Strong second harmonic generation in SiC, ZnO, GaN two-dimensional hexagonal crystals from first-principles many-body calculations

We published a new paper on the second harmonic generation(SHG) in two-dimensional hexagonal crystals SiC, ZnO and GaN. The SHG is calculated within the so called GW plus Bethe-Salpter formalism, using a real-time implementation proposed by some of us. We found that these system present a large region with a strong SHG before the absorption… Read More

Review on GW and Bethe-Salpeter for molecular systems

We just published a new review on GW and Bethe-Salpeter (BSE) for molecules. In the review we discuss electronic excitations both in TDDFT and  in the Green’s function approach.  The successes and failures of the different methods are presented. In particular we focused on charge-transfer excitations for which the photoexcited electron and the hole left… Read More