INFLUENCE OF PSEUDOCORE VALENCE-BAND HYBRIDIZATION ON THE CRYSTAL-STRUCTURE PHASE STABILITIES OF TRANSITION-METALS UNDER EXTREME COMPRESSIONS

We demonstrate that the conventional picture of crystal structure stabilities of transition metals, namely, as being determined by the degree of filling of the ''canonical'' d bands, breaks down at very high pressures. We show, by means of first-principles calculations, that for extreme compressions the pseudocore p states become broad and start to hybridize with the valence states. This results in a modification of the electronic structure and consequently unexpected crystal structures become stabilized. Simple model calculations using p- and d-canonical bands, which are allowed to hybridize with each other, predict that the bcc structure is the most stable crystallographic phase at high pressure for most of the transition elements, in agreement with our first-principles calculations. © 1994 The American Physical Society.