The semiconductor iron pyrite has recently attracted much interest again du
e to its promising capabilities for photovoltaic applications as well as a
possible material for solid-state batteries. It also shows an unusual blue
shift of the optical gap under pressure. We present a full potential total
energy calculation of iron pyrite using density functional theory with a no
n-orthogonal local orbital minimum basis scheme (K. Koepernik, H. Eschrig,
Phys. Rev. B 59 (1999) 1743). We obtain a good agreement between our calcul
ations and experimental values for the lattice constant, the positions of t
he sulfur atoms in the lattice and the bulk modulus. A study of the effect
of isotropic external pressure on the electronic structure of pyrite gives
new insight into the optical properties of pyrite. (C) 2000 Elsevier Scienc
e B.V. All rights reserved.