GW quasiparticle band structure of YH3

We present an ab initio calculation of YH3 using the GW approximation (GWA) . Although a density functional calculation incorrectly gives a metallic st ate unless we assume a very complicated structure, the self-energy correcti on with the GWA removes the band overlap, and reproduces insulating behavio r. Hence, the failure of the density-functional calculation can be attribut ed to an electronic origin. The role of the self-energy is to raise the uno ccupied Y 4d band rather than to decrease the bandwidth of the occupied H 1 s band.