Density functional (DF) electronic structure calculations for UFeX (X=Si, G
el compounds were performed using fully relativistic optimized linear combi
nation of atomic orbitals (OLCAO), relativistic general potential linear au
gmented plane wave (LAPW) and scalar relativistic augmented sphere wave (AS
W) methods. The Sf-states of uranium were assumed itinerant and treated as
band states. We confirm the experimental observation that UFeGe is a parama
gnet. On the other hand, our extensive DF calculations including the fixed-
spin-moment method predict an instability of the paramagnetic state of UFeS
i in the orthorhombic TiNiSi structure. Since both UFeSi and UFeGe are isoe
lectronic with respect to the number of valence electrons the actual ground
states result from a subtle interplay between the band filling of the free
electron background (s-, p-, and U-d electrons) and the iron bonding bands
on one side and the covalency (hybridization) between bonding predominantl
y 3d states of iron and antibonding predominantly 5f-states of uranium on t
he other side. (C) 2001 Elsevier Science B.V. All rights reserved.