A new crystal family of GaNGeC quaternary compounds including direct band gap semiconductors and metals

Predicting the crystal structures of novel quaternary compounds can be challenging, as there are only a few stable structures among numerous possible ones. Using a recently developed particle swarm optimization-based crystal structure prediction method and the first-principles calculation method, we discover a new crystal family of quaternary GaNGeC compounds, including six direct band gap semiconductors (denoted as S-1, S-2, S-3, S-4, S-5 and S-6) and two metals (denoted as S-7 and S-8); these compounds can potentially be employed in optoelectronic and energy applications. S-1, S-2, S-3, S-4, S-5 and S-6 exhibit high optical absorption coefficients in the visible region. Moreover, S-1, S-2, S-3, S-4 and S-5 possess band edge positions of the valence band maximum and conduction band minimum that are suitable for photocatalytic overall water splitting in the visible region.