Date: 28 April 2023
Location: Zoom event

On Friday April 28 at 2pm CEST, Alberto Guandalini from the University of Rome La Sapienza will give a seminar of the ETFS (European Theoretical Spectroscopy Facility) series.

The title of the talk is “Efficient many-body perturbation theory calculations in 2D materials via the interpolation of the screened interaction: GW corrections and EELS spectra”. 

All ETSF members will receive an email with a zoom link a couple of days before the seminar. If you are not an ETSF member and you would like to follow the seminar, please send an email to
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Many-body perturbation theory methods are able to accurately predict quasiparticle (QP) and spectroscopic properties of several classes of materials. However, the calculation of the QP band structure of 2D materials is known to require a very dense BZ sampling. For 2D semiconductors, large q-point grids are required to describe the sharp q-dependence of the dielectric matrix in the long-wavelength limit (q → 0). Additionally, 2D Dirac-like systems (e.g. free-standing graphene) also show peculiar dielectric features originating from the linear dispersion of the bands close to the Dirac point.
In this talk, I will first describe a new methodology able to drastically improve the convergence of the QP corrections in 2D semiconductors with respect to the BZ sampling by combininga Monte Carlo integration method with an interpolation scheme able to describe the sharp dispersion of the dielectric function.

Then, I will show how to integrate the new methodology with a multi-pole expansion of the frequency dependence of the screening, able to reach the accuracy of full-frequency methods with a coarse sampling of the frequency space.

The combined approach will be used to obtain accurate results for graphene QP band structure. The latter is finally  used  to calculate electron energy loss spectra (EELS) of graphene at finite momentum transfer via the Bethe-Salpeter equation (BSE), showing excellent agreement with recent experimental data provided that the electron-hole interaction is properly taken into account.