Guseinov, Israfil Isa2025-01-272025-01-2720070259-97911572-8897https://doi.org/10.1007/s10910-006-9090-0https://hdl.handle.net/20.500.12428/21928In this study, the combined Hartree-Fock (HF) and Hartree-Fock-Roothaan equations are derived for multideterminantal single configuration states with any number of open shells of atoms, molecules and nuclei. It is shown that the postulated orbital-dependent energy and Fock operators are invariant to the unitary transformation of orbitals. This new methodology is based entirely on the spin-restricted HF theory. As an application of combined open shell theory of atomic-molecular and nuclear systems presented in this paper, we have solved Hartree-Fock-Roothaan equations for the ground state of electronic configuration C(1s(2)2s(2)2p(2)) using Slater type orbitals as a basis.eninfo:eu-repo/semantics/closedAccessHartree-Fock theoryopen-shell systemsmultideterminantal statesArticle42217718910.1007/s10910-006-9090-0Q2WOS:0002479909000062-s2.0-34547239366Q2