  The layered van der Waals trichalcogenide NiPS3 has attracted widespread
attention due to its unique optical, magnetic, and electronic properties. The
complexity of NiPS3 itself, however, has also led to ongoing debates regarding
its characteristics such as the existence of self-doped ligand holes. In this
study, X-ray absorption spectroscopy and resonant inelastic X-ray scattering
have been applied to investigate the electronic structure of NiPS3. With the
aid of theoretical calculations using the charge-transfer multiplet model, we
provide experimental evidence for NiPS3 being a Mott-Hubbard insulator rather
than a charge-transfer insulator. Moreover, we explain why some previous XAS
studies have concluded that NiPS3 is a charge-transfer insulator by comparing
surface and bulk sensitive spectra.
