Calculating optical spectra including excitonic effects: a step-by-step guide

This tutorial guides you through the workflow of a calculation of the optical spectrum of a given material by solving the Bethe-Salpeter equation. Specifically, we will use bulk h-BN as an example.

Before starting, you need to obtain the tarballs for hBN. See instructions on the main tutorials page.

The target quantity in a Bethe-Salpeter calculation is the macroscopic dielectric matrix ε_M. The following quantities/steps are needed to obtain ε_M:

The optical absorption spectrum corresponds to Imε_M(ω). Following this scheme we go through the flow of a calculation:

Step 1: Static screening

Use the SAVE folders that are already provided and type:

$ cd YAMBO_TUTORIALS/hBN/YAMBO

Follow the Static screening module and then return to this tutorial

Step 2: Bethe-Salpeter kernel

Follow the module on Bethe-Salpeter kernel and return to this tutorial

Step 3: Diagonalisation of the excitonic Hamiltonian

This is the step in which you obtain the spectra. Mathematically this implies solving a large eigenvalue problem. In this case we are going to directly diagonalise the matrix, but there are different numerical approaches available in Yambo. The difference between the various other approaches and when they should be used is the object of one of the next tutorials.

Follow the module on Bethe-Salpeter solver: diagonalization then return to this tutorial

Step 4: Include previous quasiparticle (GW) results

Follow the module on Including quasiparticle database and return to this tutorial