Spin-restricted density functional approach to the open-shell problem

Open-shell one-electron equations are derived by application of Roothaan's coupling operator technique to the variational procedure of finding the Kohn-Sham orbitals and minimizing the energy of an open-shell system, represented within the density functional vector coupling scheme. The final equations are presented in a form suitable for standard quantum-chemical codes using finite basis set Kohn-Sham calculations. Examples of multiplets for which the theory is applicable are discussed.