Quasiparticle energy of semicore d electrons in ZnS:: Combined LDA+U and GW approach

We present a first-principles study of quasiparticle energies in ZnS, with particular emphasis on the semicore d electrons that are located too shallow by similar to 2.8 eV compared to experiment in the local density approximation (LDA). Although the many-body correction in the GW approximation pulls down the d band, the correction (-0.7 eV) is too small to reproduce measured values. The LDA+U method also shifts the d band down compared to LDA. With a reasonable choice of U, d-state energy in agreement with experiment may be achieved. Subsequent quasiparticle calculation within the GW approximation performed to the LDA+U mean-field solution, however, pushes the d band back close to the GW result. These results show that the standard GW method is insensitive to the reference mean-field Hamiltonian for this class of materials and suggest that going beyond GW may be needed for an accurate description of the d electron level in this system.