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
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
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
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
A new version of the Lumen code is available online. It includes spin-orbit coupling, the possibility to use polarised light and the real-time Bethe-Salpeter equation (RT-BSE). Notice that the RT-BSE is limited to small systems or a small number of G-vectors in the screened-exchange due to its computational time. New tutorials on spin-orbit coupling and… Read More
At CINaM together with Andres Saul and Hans-christian Weissker we are organizing a series of lectures on DFT and the Quantum Espresso code. The course will cover standard DFT, functionals, psedo-potentials, surfaces, STM images, structure optimization, etc.. Teaching material and lecture notes can be downloaded here: DFT and Quantum Espresso 1 DFT and Quantum Espresso… Read More
Performing RPA calculations with yambo in large systems can be a problem due to the memory requirement. In fact the code does not distribute the dielectric constant at the different frequencies among the processors. The solution is to run different calculations for each frequency of the dielectric constant and then joind the outputs. Here my… Read More
Here I present the BSE input file for yambo and I will discuss the meaning of each parameter. For a discussion on convergence issues see my post: Reasonable parameters for Yambo calculations. To generate this input type yambo -o b -k sex -y d -p p -V qp. I will not discuss the parameters relative… Read More
Example of a yambo input file for GW calculation in a solid. In order to generate the following input file you can use the command “yambo -g n -p p -V par” with yambo 4.0.2 (and with yambo 3.4.2 “yambo -g n -p p”). gw0 # [R GW] GoWo Quasiparticle energy levels ppa #… Read More
Here I report some advices to choose reasonable parameters in order to converge different kind of calculations with the Yambo code. The following parameters are a reasonable recommendation. However you have to remember that convergence can be different from system to system, so you should check your calculations and not use the following parameters blindly…. Read More