CONTROLLING ORBITAL COLLAPSE FROM INSIDE AND OUTSIDE A TRANSITION ELEMENT

We report a study of bimodal behaviour of atomic wavefunctions for a t ransition element (Cr) and how this behaviour can be controlled and ev en turned into single-mode character either by (i) varying the effecti ve nuclear charge for nonintegral values, or (ii) placing the atom in a spherical cavity of adjustable radius. Our conclusions have relevanc e to the emergence of valence instabilities for transition metals in t he solid state. Also it is shown that the very existence of the bimoda l wavefunctions provides an explanation for the frequently experienced instability of self-consistent field algorithms when a double-valley potential occurs, and suggestions are made on how to improve the numer ical procedure for such calculations.