The wavefunction generated by the scaled one-electron Hamiltonian (soeh) model has been modified further by including all single excitations from the space of thesoeh function. A perturbation-variation ansatz has been invoked for obtaining the corresponding energy correction (ΔE2). [E(soeh)+ΔE2] is shown to reproduceE(Roothaan) very closely. It has been demonstrated that by making ΔE2 stationary with respect to change in μ results. The correctedsoeh [E(soeh)+ΔE2] is shown to be quite useful for the calculation of geometrical parameters of open-shell systems even though it lacks the ‘upper-boundedness’ exhibited byE(soeh).
Volume 134, 2022
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