The GW and Bethe-Saltpeter Equation (GW-BSE) is a Green's function based approach, that goes beyond the conventional Density functional theory (DFT) to describe excited states of electrons in materials. However, over the past few decades, most ab initio GW calculations used have been confined to small units of cells of bulk-like materials due to the extreme computational demands of the approach. In this talk, I will show my collaborative efforts to develop a new open-source software that permits large scale GW calculations more efficiently: our GW software is interfaced with the ab-initio plane wave pseudopotential OpenAtom software that uses the Charm++ parallel framework.
I will also briefly discuss my ongoing research on topological crystalline insulators, which are a new class of topological materials where electronic surface states are topologically protected along certain crystallographic directions by crystal symmetry. I will show that, without any external perturbation, both massless Dirac fermions protected by the crystal symmetry and massive Dirac fermions with crystal symmetry breaking can coexist on a single surface.