Effect of correlation and orbital-dependent generalized exchange on the equilibrium geometry of the H2O molecule in the LCGTO-LDA method

Abstract

An orbital-dependent, generalized exchange was implemented, as a post-SCF self-consistent field correction term, within the linear combination gaussian type orbital local density approximation, LCGTO-LDA, methodology. Equilibrium geometries of H₂O were calculated with and without a Vosko, Wilks and Nasair (VWN) correlation functional. The role of relaxation was examined by comparing the result from a post-SCF correlation correction (‘unrelaxed’) with the result from correlation in the one-electron Hamiltonian; the relaxed and unrelaxed results were nearly identical. The orbital-dependent correction terms significantly improved the predicted bond length and angle compared with the simple LDA calculation, but increased the force constant f_θθ, taking it further from experiment.