Heterogeneous nanostructured materials are widely used in a variety of optoelectronic devices, including solar cells. However, due to their heterogeneous nature, these materials contain nanoscale interfaces exhibiting structural defects that can affect the performance of these devices. It is very challenging to identify these defects in experiments, so a team of researchers at the Department of Energy’s Argonne National Laboratory and the University of Chicago decided to run a series of atomistic calculations at Lawrence Berkeley National Laboratory’s National Energy Research Scientific Computing Center (NERSC) to find the root cause of defects in two commonly used semiconductor materials—lead selenide (PbSe) and cadmium selenide (CdSe)—and provide design rules to avoid them.