Correlated Linear Response Calculations of the C6 Dispersion Coefficients of Hydrogen Halides

What is it about?

Three correlated linear response theory methods – the second order polarization propagator approximation (SOPPA), the second order polarization propagator approximation with coupled cluster singles and doubles amplitudes, SOPPA(CCSD), and multiconfigurational self-consistent field (MCSCF) linear response theory – were used to determine the electric dipole polarizabilities at imaginary frequencies of the hydrogen halides HX (with X = F, Cl, Br and I). The dynamic polarizabilities were subsequently used to calculate the C6 dispersion coefficient for a pair of interacting HX molecules via numerical integration of the Casimir-Polder formula. The dependence of the polarizabilities, their frequency dependence and C6 coefficients on the one-electron basis set, the level of correlation and zero-point vibrational corrections was studied. Furthermore it was investigated whether relativistic effective core potentials (RECP) could be employed in such calculations. It was found that SOPPA(CCSD) and MCSCF calculations with large active spaces using basis sets of at least double augmented quadruple zeta quality give comparable results which in particular for SOPPA(CCSD) are in close agreement with the available experimental values. Furthermore it could be shown that the results of the RECP calculations are in close agreement with the all electron calculations.

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