Electronic Spectroscopy

We are developing ab initio methods based on density functional and many body perturbation theory to compute optoelectronic properties of materials and to predict electronic spectra. In particular, we develop and maintain the WEST code, a massively parallel software for large scale electronic structure calculations based on many-body perturbation theory.

Photoluminescence and absorption spectra

We developed ab initio approaches to compute vibrationally resolved optical spectra of large systems, with focus on point defects in semiconductors. We implemented the calculation of excited state analytical nuclear forces for both spin-conserving and spin-flip time-dependent density functional theory (TDDFT) in the WEST code, thus enabling the study of excited state potential energy surfaces. We use the Huang-Rhys theory to describe the coupling between the vibrational and the electronic degrees of freedom in the optical processes, and the generating function approach to compute vibrationally resolved spectra. We investigated the vibrationally resolved photoluminescence, absorption, and photo-ionization spectra of spin-defects in semiconductors, e.g. the nitrogen-vacancy center in diamond and divacancy centers in silicon carbide.


Quantum Vibronic Effects on the Electronic Properties of Solids and Molecules

We have been exploring several approaches to investigate vibronic effects on the electronic properties of solids and molecules. One approach uses density functional or density matrix perturbation theory and efficiently combines the computation of electron–electron and electron–phonon self-energies. Another approach combines path integral first principles molecular dynamics (FPMD) with a colored noise thermostat. We have used these methods to study molecular crystal and several carbon systems, including amorphous carbon, diamond and point defects in diamond.


Data Collections

The WEST Data Collections provide open web-based access to electronic structure properties computed with WEST. Explore the GW100 and GW-SOC81 sets.

GW and BSE calculations

We have developed ab initio approaches to compute optical absorption and emission spectra of molecules and solids, which are suitable for the study of large systems and give access to spectra within a wide energy range. For absorption spectra, the quantum Liouville equation is solved iteratively within first order perturbation theory, with a Hamiltonian containing a static self-energy operator. For emission spectra, we use a spectral decomposition of the static dielectric matrix as a basis for the frequency dependent density-density response function. Explicit calculations of single particle excited states and inversion and storage of dielectric matrices are avoided using techniques based on Density Functional Perturbation Theory.