Localized and bandlike valence-electron states in FeS2 and NiS2

Photoemission energy distributions for 20<~hν<~50eV for semiconducting FeS2 (fool's gold) show a narrow, ∼1 eV wide, localized uppermost valence level, whereas the corresponding levels of semiconducting NiS2 are broad (∼3.5 eV) and bandlike. Self-consistent-field Xα cluster calculations indicate that this level in FeS2 is the 3d-like t2g state, while in NiS2 the uppermost level is the more bandlike eg state, with t2g states about 2 eV lower that overlap the broad S 3p-derived valence bands. © 1974 The American Physical Society.