Alfredo Pasquarello

Alfredo Pasquarello effectue ses études en physique à l'Ecole normale supérieure de Pise et à l'Université de Pise et obtient leurs diplômes respectifs en 1986. Il obtient le titre de Docteur ès sciences à l'EPFL en 1991 avec une thèse portant sur les transitions à plusieurs photons dans les solides. Ensuite, il effectue des recherches post-doctorales aux Laboratoires Bell (Murray Hill, New Jersey) sur les propriétés magnétiques des fullerènes de carbone. En 1993, il rejoint l'Institut romand de recherche numérique en physique des matériaux (IRRMA), où sa recherche porte sur des méthodes de simulation ab initio. En 1998, le Prix Latsis de l'EPFL lui est decerné pour son travail de recherche portant sur les matériaux à base de silice désordonnée. Bénéficiant de plusieurs subsides du Fonds National, il constitue ensuite sa propre équipe de recherche à l'IRRMA. En juillet 2003, il est nommé Professeur en Physique théorique de la matière condensée à l'EPFL. Actuellement, il dirige la Chaire de simulation à l'échelle atomique.

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PHYS-207(c): General physics : quanta

Le cours traite les ondes électromagnétiques (optique géométrique et optique physique) et donne une introduction à la physique quantique.

PHYS-403: Computer simulation of physical systems I

The two main topics covered by this course are classical molecular dynamics and the Monte Carlo method.

PHYS-819: First-principles modelling of defects in solids

This Summer School aims to provide an overview of the latest advances in the theory and simulation of defects in solids. The event consists of invited talks given by internationally renowned experts in the field, as well as networking opportunities and social events.

Théorie de la fonctionnelle de la densité

La théorie de la fonctionnelle de la densité (DFT, sigle pour Density Functional Theory) est une méthode de calcul quantique permettant l'étude de la structure électronique, en principe de manière ex

Dynamique moléculaire

La dynamique moléculaire est une technique de simulation numérique permettant de modéliser l'évolution d'un système de particules au cours du temps. Elle est particulièrement utilisée en sciences de

Premier principe

En philosophie, un premier principe ou principe premier désigne soit une proposition dont dérive toutes les autres propositions du domaine considéré soit une cause de toutes les autres choses du do

Many-body screening effects in liquid water

Arnaud Guillaume Lorin, Alfredo Pasquarello, Igor Reshetnyak

The screening arising from many-body excitations is a crucial quantity for describing absorption and inelastic X-ray scattering (IXS) of materials. Similarly, the electron screening plays a critical role in state-of-the-art approaches for determining the fundamental band gap. However, ab initio studies of the screening in liquid water have remained limited. Here, we use a combined analysis based on the Bethe-Salpeter equation and time-dependent density functional theory. We first show that absorption spectra at near-edge energies are insufficient to assess the accuracy by which the screening is described. Next, when the energy range under scrutiny is extended, we instead find that the IXS spectra are highly sensitive and allow for the selection of the optimal theoretical scheme. This leads to good agreement with experiment over a large range of transferred energies and momenta, and enables establishing the elusive fundamental band gap of liquid water at 9.3 eV. Electron screening is crucial to interpret inelastic X-ray scattering experiments in materials. Here the authors use a combined analysis based on the Bethe-Salpeter equation and time-dependent density functional theory to calculate the dielectric function and obtain the band gap of liquid water.

NATURE PORTFOLIO2023

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Polaron hopping through piecewise-linear functionals

Stefano Falletta, Alfredo Pasquarello

We use piecewise-linear functionals to study the polaron energy landscape and hopping rates in beta-Ga2O3, which we adopt as an example of an anisotropic material hosting multiple polaronic states. We illustrate various functionals for polaron localization, including a hybrid functional and two types of semilocal functionals, and discuss how to ensure the piecewise-linearity condition. Then, we determine the formation energies of stable polarons, and show that single-site and multisite polaronic states can be found in close energetic competition. We calculate the hyperfine and superhyperfine parameters associated with each polaron, and discuss the comparison with experiment. Next, we perform nudged-elastic-band calculations to determine energy landscapes and hole transfer rates of all first-nearest-neighbor polaron hoppings. We show that when the piecewise-linearity condition is ensured polaron properties are robust upon variation of the functional adopted, including formation energies, energy barriers, and charge transfer rates. This supports the use of semilocal functionals for calculating polaron transport properties.

AMER PHYSICAL SOC2023

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Accurate and efficient band-gap predictions for metal halide perovskites at finite temperature

Thomas Bischoff, Patrick Gono, Alfredo Pasquarello, Aleksei Tal, Haiyuan Wang

We develop a computationally efficient scheme to accurately determine finite-temperature band gaps for metal halide perovskites belonging to the class ABX(3) (A = Rb, Cs; B = Ge, Sn, Pb; and X = F, Cl, Br, I). First, an initial estimate of the band gap is provided for the ideal crystalline structure through the use of a range-separated hybrid functional, in which the parameters are determined non-empirically from the electron density and the high-frequency dielectric constant. Next, we consider two kinds of band-gap corrections to account for spin-orbit coupling and thermal vibrations including zero-point motions. In particular, the latter effect is accounted for through the special displacement method, which consists in using a single distorted configuration obtained from the vibrational frequencies and eigenmodes, thereby avoiding lengthy molecular dynamics. The sequential consideration of both corrections systematically improves the band gaps, reaching a mean absolute error of 0.17 eV with respect to experimental values. The computational efficiency of our scheme stems from the fact that only a single calculation at the hybrid-functional level is required and that it is sufficient to evaluate the corrections at the semilocal level of theory. Our scheme is thus convenient for the screening of large databases of metal halide perovskites, including large-size systems.

NATURE PORTFOLIO2022

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