How to choose the input parameters

In the previous tutorial, you have been guided step-by-step through the calculations of the optical spectrum of bulk hBN by solving the Bethe-Salpeter equation. The values for the relevant input parameters have then been given to you.

In this tutorial you will learn how to choose those parameters. These parameters are related either to the truncation of infinite sums or to the approximations of infinitesimal with small, but finite quantities. A wrong choice of these parameters can lead to inaccurate or even physically wrong results. One then needs to run a series of calculations by changing the parameters till the results are converged , meaning they are changing by a negligible amount.

Note that all the following operations can be automated. A useful python-based interface to yambo, yambopy, can be used for this purpose. It is worth however to go at least once through the pain of a 'by-hand' convergence study so to better understand the automated process for few of those variables.