DENSITY-FUNCTIONAL THEORY FOR EXCITED-STATES AND SPECIAL SYMMETRIES

For Hamiltonians which are invariant under a group of transformations, one can restrict the search for the energy eigenstates in spaces whos e functions transform according to the irreducible representations of the group. However, the construction of a Slater determinant to repres ent the equivalent noninteracting system of DFT, with the proper trans formation properties, is not trivial. Further such a determinant does not always exist. The use of the subspace theory [J. Phys. C 12, 5419 (1979)] developed initially to deal with the density functional theory for excited states overcomes this difficulty and an equivalent system of one-particle Kohn and Sham equations is derived with nonintegral o ccupation numbers in the expression of the density. In this article, w e derive the explicit form of the subspace density for systems with sp herical symmetry. The density does not depend on the Clebsch-Gordan co efficients, but only on the radial part of the orbitals entering the d eterminant of the noninteracting state with largest 1. (C) 1997 John W iley & Sons, Inc.