We describe an efficient numerical implementation of the Bethe-Salpeter equation to obtain the excitonic spectrum of semiconductors. This is done on the electronic structure calculated either at the simplest tight-binding level or through density functional theory calculations based on local orbitals. We use a simplified model for the electron-electron interactions which considers atomic orbitals as point-like orbitals and a phenomenological screening. The optical conductivity can then be optionally computed within the Kubo formalism. Our results for paradigmatic two-dimensional materials such as hBN and MoS2, when compared with those of more sophisticated first-principles methods, are excellent and envision a practical use of our implementation beyond the computational limitations of such methods.

Program summary: Xatu CPC Library link to program files: https://doi .org /10 .17632 /kj4rt95pvc .1 Developer’s repository link: https://github .com /alejandrojuria /xatu Licensing provisions: GPLv3 Programming language: C++, Fortran, Python

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