Excited states Forces with BSE

Photochemical processes are fundamental to wide range of physical and chemical phenomena. However many of these processes involve structural changes, e.g. fragmatization,formation or elimination of defects. In order to understand these photo-induced structural changes using first principles calculations, we need to calculate the interatomic forces in the excited state accurately and efficiently. By combining the many-body Green’s function (GW) and the Bethe-Salpeter equation formalism. We present a practical method for computing the excited state forces, which is implemented with the help of the Quantum espresso package and the GWL code. In order to test this technique we used the CO molecule, the results proved to be in agreement with the experiment.