LOCALIZED ORBITAL THEORY OF ELECTRONIC-STRUCTURE - A SIMPLE APPLICATION

Galli and Parrinello introduced a formulation of electronic-structure theory based on the optimization of a set of orbital-like functions ex actly equal in number to the number of electrons in the system, in con trast to conventional theories based on the occupied subspace of a lar ger variational Hilbert space. We have applied this formulation to a s ystem sufficiently simple to permit study of its inner workings. We fi nd that the unapproximated theory can be applied to delocalized, metal lic systems, but the optimized functions, considered as a function of the strength of a localizing lattice potential, are not well localized for realistically weak (pseudo) potentials. Perhaps more importantly, we find that the formulation can be extremely numerically sensitive, rendering approximations made within the formulation potentially dange rous.