The activity is done in collaboration with E. Perfetto and G. Stefanuccci (Università di Roma Tor Vergata, Italy), C. Attaccalite  (CINaM - CNRS, Marseille, France), and M. D'Alessandro (ISM - CNR, Roma, Italy)

The image on the right shows the computed exciton TR-ARPES bulk lithium fluoride after the action of a pump laser pulse. In the simulation the pump laser pulse is resonant with the energy of the 1s exciton. The exciton photoemission signal (upper panel) is a replica of the valence band signal (lower panel) weighted by the excitonic wave–function. The distance from the conduction band minima corresponds to the binding energy of the exciton. Image from Phys. Rev. Mat. 3, 124601 (2020)

Related publications:

• Phys. Rev. Mat. 5, 083803 (2021)

• Phys. Rev. Mat. 3, 124601 (2020)

• Eur. Phys. J. B 91, 171 (2018)

Work in progress

In the image on the right transient reflectivity signal of bulk silicon, computed at the Bethe-Salpeter, level due to the non-equilibrium carriers distribution at 200 fs from the maximum of the laser pulse. Image from Phys. Rev. B 93, 195205 (2016). The results of the simulations are directly compared with the signal collected by the experimental measurements performed by S. Dal Conte (Politecnico di Milano, Italy).

Davide Sangalli moved at the ISM in Montelibretti within the FIRB projec FLASH-IT, whose aim is the first principles description of out-of-equilibrium dynamics of electrons in the ultra-short (atto/femto-second) time domain. The work was done in close collaboration with the experimental group of the Politecnico di Milano.

Here a representation of the electrons and holes occupations on the band structure of bulk silicon at different time snapshots after the action of an ultra-short laser pulse. Image from EPL 110, 47004 (2015). 

Work in progress

Eigenvalue problems lie at the core of many physical applications and beyond. While often hermitian matrices (HMs) appear, more in general, broader classes of matrices need to be studied. The IsolvBSE project addresses the class of structured pseudo-hermitian matrices (SPHMs). SPHMs emerge, for example, when studying interacting particle-hole hamiltonians, whose eigenvalues and eigenvectors need to be computed to determine the optical properties of materials.

Nowadays, when SPHMs need to be solved, algorithms for non-hermitian matrices (NHMs) are frequently used. Indeed, specific algorithms for SPHMs have been developed only for full diagonalization. For the case of particle-hole hamiltonians, a specific iterative algorithm for SPHMs has also been developed. However, while the algorithm has been very successful, it does not give access to eigenvalues and eigenvectors of the matrices, which are often also needed.

IsolvBSE will develop a novel algorithm able to provide, via an iterative approach, a subset of the eigenvalues and eigenvectors, specific for SPHMs.  This novel algorithm for SPHMs will be directly coded inside the SLEPc library, thus ensuring that it will be made publicly available to the community and distributed. Moreover we will call it via a simple subroutine, which will be embedded in the yambo code. The latter is already interfaced with the SLEPc library, and this structure will ensure a smooth transition towards realistic applications in the future.

The target of the project is the investigation, with extreme temporal resolution, of the molecular processes initiated by the interaction of ionizing radiation with biologically relevant molecules. The main objective is to identify and control at molecular level the early steps of light-driven processes of primary importance in photochemistry and photobiology, which typically evolve on timescales ranging from theattosecond domain of purely electron dynamics, to the hundreds of femtosecond domain of nuclear dynamics. The experimental strategy is based on the combination of advanced time-resolved techniques, characterized by extreme temporal resolution (from a few femtoseconds to a few hundreds of attoseconds), with synchrotron-based spectroscopic techniques to unravel the molecular mechanisms leading to photo-protection or damage of bio-relevant molecules. Advanced numerical modelling, based on a novel and unique theoretical approach which takes into account the atomistic details of the molecular structure, the action of the extreme-ultraviolet and ultrashort excitation, electron correlation effects and the coupling between electronic and nuclear degrees of freedom, will support and guide the experimental activity.

An ad-hoc version of the yambo code was developed for dealing with isolated systems. If you are interested please download the phys-cichroism branch of my personal for of the yambo code: https://github.com/sangallidavide/yambo/tree/phys-dichroism .

External links:

• https://www.ism.cnr.it/en/research/projects/item/156-predicting-and-controlling-the-fate-of-bio-molecules-driven-by-extreme-ultraviolet-radiation.html

The TUMIEE cost action

NFFA (Nanoscience Foundries and Fine Analysis – Europe H2020-INFRAIA-2014-2015, Grant Agreement No. 654360) projects.