Author Archives: attacc

Luminescence of hexagonal boron nitride explained

Luminescence of hexagonal boron nitride (hBN) has puzzled researchers for long time. In standard solid state physics textbooks direct band gap semiconductors are considered efficient light emitters while indirect ones are regarded as inefficient. Hexagonal boron nitride seems to defy this rule. In fact hBN emits light in the ultraviolet with an efficient comparable to… Read More

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

OPTEL2D: Opto-electronic properties of 2D Transition Metal Dichalcogenides with DFT and post-DFT simulations

Our Prace research project OPTEL2D “Opto-electronic properties of 2D Transition Metal Dichalcogenides with DFT and post-DFT simulations” has been accepted, and we got 49.5 million core hours on Marconi – KNL.     Here the project description: “Two-dimensional (2D) and layered materials possess novel combinations of electronic and optical properties and thus present a unique… Read More

Full professor position at CINaM (Marseille)

The Interdisciplinary Nanoscience Center of Marseille (CINaM), a laboratory working  under the joint authority of the Centre National de la Recherche Scientifique (CNRS)and the Aix-Marseille University (AMU), invites applications for a full-time endowed position at a Professor level. The research activity will be developed in the Theory and Computer Simulation department, in relation with experimental… Read More

Two-photon absorption in two-dimensional crystals

In this work we combine tight-binding calculations of the two-photon transition probability with sophisticated ab-initio real-time Bethe-Salpeter simulations of the two-photon resonance third-order susceptibility. This combination is a unique feature of this work: on the one hand the tight-binding calculations allow us to identify the symmetry properties of the excitons, on the other hand the… Read More

Role of excitonic effects in nonlinear optical properties of 2D materials

My collaborator Myrta Grüning gave a very interesting talk about the role of excitons in non-linear optical properties of 2D materials at the OSI 2017 conference. She discusses  both second and third harmonic generation in low dimensional nanostructures. Slides of her talk are available here .

GDR-REST: second general meeting in Porquerolles

The second general meeting of the GDR-REST will be held in the Porquerolles island from 22.05. to 25.05.2018. This meeting aims to bring together different communities of theoretical spectroscopy which are/were historically separated, but unified under a very precise and important subject: the excited-states spectroscopy of variety of systems (for both weakly and strongly correlated… Read More

Invisible excitons in hexagonal Boron Nitride

New talk for the conference “2D layered materials for opto-electronics: a theoretical/computational perspective” in Rome. In this work we study excitations in hexagonal Boron Nitride that are invisible in linear optical response. We show that these dark states can be measured with other spectroscopic techniques and they play an important roles in the luminescence response… Read More

GW correction on an arbitrary point of the Brillouin zone with Yambo

Here I show how to calculate GW correction for a generic k-point not included in the original grid used to perform a GW calculations using Yambo 4.2. This method allows to obtain the GW correction without the need of recalculate the full dielectric constant used in the initial calculation. As example I will take 2-dimensional… 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