Accuracy of energy-adjusted quasirelativistic pseudopotentials: a calibration study of XH and X2(X = F, Cl, Br, I, At)

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Abstract
Quasirelativistic pseudopotential calibration calculations have been performed for the halogen monohydrides XH and homonuclear dimers X2 (X = F, Cl, Br, I, At) using large uncontracted basis sets at various levels of theory: self-consistent field calculations with subsequent single-reference coupled-cluster singles and doubles calculations including a perturbative estimate for the contribution of triples as well as multi-configuration self-consistent field calculations with subsequent multi-reference averaged coupled-pair functional calculations. Spin-orbit contributions were derived from singles and doubles configuration interaction studies. The pseudopotential results are compared with scalar relativistic self-consistent field all-electron calculations using the Douglas-Kroll-Hess Hamiltonian as well as with experimental data. The accuracy of the pseudopotential-derived molecular constants in comparison with all-electron (experimental) data is better than 0·018 (0·010) Å for bond lengths, 26 (34) cm−1 for vibrational constants and 0·04 (0·20) eV for binding energies. Predictions for the properties of the astatine compounds HAt and At2 are made.