molecular electronic configuration.For example,an (eg)configuration of Doh molecule gives the termsAg E2g,andA2g. A closed-shell configuration gives rise to a single nondegenerate term whose multiplicity is I and whose symmetry species is the totally symmetric. SCF-MO Wave Functions for Open-Shell States. For SCF MO calculations of closed-shell states of molecules and atoms,electrons paired with each other almost given precisely the same spatial orbital function.A Hartree-Fock wave function in which electrons whose spins are paired occupy the same spatial orbital is called a restricted Hartree-Fock(RHF)wave function For open-shell states,two different approaches are widely used. Restricted Open-Shell Hartree-Fock(ROHF)Method In the ROHF method,electrons that are paired with each other are given the same spatial orbital function.For example,the ROHF wave function of the Li ground state is |sls2s1,where the two Is electrons occupy the same spatial MO.The 2s electron in this ROHF function has been given spin a. Restricted Open-Shell Hartree-Fock(ROHF)Method Since electron with the same spin tend to keep away from each other (Pauli repulsion),the interaction between the 2sa and Isa electrons differs from the interaction between the 2sa and IsB electrons,and it seems reasonable to give the two Is electrons slightly different spatial orbitals,which we call Is and Is'.This gives the unrestricted Hartree-Fock (UHF)wave function for the Li ground state as |1s1s'2s, where Is Is'.In a UHF wave function,the spatial orbitals of spin-a electrons are allowed to differ from those of spin-B electrons Comparison of ROHF with UHF The UHF wave function gives a slightly lower energy than the ROHF wave function and is much more useful in predicting molecular electronic configuration. For example, an (e1g) 2 configuration of D6h molecule gives the terms 1 A1g, 1 E2g, and 3 A2g. A closed-shell configuration gives rise to a single nondegenerate term whose multiplicity is 1 and whose symmetry species is the totally symmetric. SCF-MO Wave Functions for Open-Shell States. For SCF MO calculations of closed-shell states of molecules and atoms, electrons paired with each other almost given precisely the same spatial orbital function. A Hartree-Fock wave function in which electrons whose spins are paired occupy the same spatial orbital is called a restricted Hartree-Fock (RHF) wave function. For open-shell states, two different approaches are widely used. Restricted Open-Shell Hartree-Fock (ROHF) Method In the ROHF method, electrons that are paired with each other are given the same spatial orbital function. For example, the ROHF wave function of the Li ground state is |1s1s2s |, where the two 1s electrons occupy the same spatial MO. The 2s electron in this ROHF function has been given spin α. Restricted Open-Shell Hartree-Fock (ROHF) Method Since electron with the same spin tend to keep away from each other (Pauli repulsion), the interaction between the 2sα and 1sα electrons differs from the interaction between the 2sα and 1sβ electrons, and it seems reasonable to give the two 1s electrons slightly different spatial orbitals, which we call 1s and 1s′. This gives the unrestricted Hartree-Fock (UHF) wave function for the Li ground state as |1s1s'2s | , where 1s ≠ 1s′. In a UHF wave function, the spatial orbitals of spin-α electrons are allowed to differ from those of spin-β electrons. Comparison of ROHF with UHF The UHF wave function gives a slightly lower energy than the ROHF wave function and is much more useful in predicting