Application of spin-restricted open-shell Kohn-Sham method to atomic and molecular multiplet states

A recently proposed spin-restricted open-shell Kohn-Sham (ROKS) method is a pplied to investigate various atomic and molecular multiplet states. A wide range of multiplets is considered: multiplet terms for which the spin-rest ricted open-shell theory of Roothaan applies, as well as state situations w hich cannot be described by Roothaan's theory (e.g., states of square cyclo butadiene, etc.). Problems associated with the use of approximate density f unctionals and possible perspectives of the ROKS method are discussed. (C) 1999 American Institute of Physics. [S0021-9606(99)30101-X].