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    Öğe
    An alternative approximation to state-specific multireference second-order Brillouin-Wigner perturbation theory: size-extensivity correction
    (Springer, 2013) Aksu, H.
    State-specific, multireference, second order, Brillouin-Wigner perturbation theory is examined provided that providing a size-extensive correction to the electron correlation problem for systems that demand the use of a multireference function. We derived the renormalization term. An important aspect of this renormalization term is to cancel the non-physical terms. The computer implementations are made for bond breaking process in the ground states of the diatomic hydride using the two configuration state functions. We have achieved improved results. The results are compared with the rigorously size-extensive methods such as, MOller-Plesset perturbation theory, that is, MP2, full configuration interaction and allied methods using the same basis sets.
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    Öğe
    Application of combined Hartree-Fock-Roothaan theory to atoms with an arbitrary number of closed and open shells of any symmetry
    (Springer Wien, 2007) Guseinov, Israfil Isa; Mamedov, B. A.; Ertuerk, M.; Aksu, H.; Sahin, E.
    The applicability of a combined open-shell Hartree-Fock theory of atomic-molecular and nuclear systems to the states of a single configuration which has the arbitrary symmetry of open shells is explicitly demonstrated by calculations based on the combined Hartree-Fock-Roothaan equations for atoms. As examples of an application of the combined theory using single-zeta Slater-type basis sets, the calculations have been performed for the lowest states of the lowest and excited electronic configurations of carbon and nitrogen atoms containing one-, two- and three-open shells. For the case of single-open shells for carbon and nitrogen atoms, the double-zeta basis-set calculations are also presented. The results of computer calculations for the orbitals, kinetic and total energies, linear combination coefficients and virial ratios are given.
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    Öğe
    Calculation of negative ions of B, C, N, O and F using noninteger n Slater type orbitals
    (Chinese Chemical Soc, 2008) Guseinov, Israfil Isa; Ertuerk, M.; Sahin, E.; Aksu, H.; Bagci, A.
    Combined Hartree-Fock-Roothaan calculations have been performed using noninteger n Slater type orbitals for the ground states of the lowest electron configurations 1s(2)2s(2)2p(n) (2 <= n <= 6) for negative ions of B, C, N, O and F. These results are compared with the corresponding results obtained from the use of integer n Slater type orbitals. All of the nonlinear parameters are fully optimized. The results of calculation of coupling-projection coefficients, orbital and total energies and virial ratios are presented. It is shown that the noninteger n Slater type orbitals, in general, improve the orbital energies.