Theoretical dissociation energies for the alkali and alkaline-earth monofluorides and monochlorides

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Abstract
Ab initio calculations using self‐consistent‐field and correlated wave functions are used to determine accurate spectroscopic parameters (re, ωe, D0) for the alkali and alkaline‐earth monofluorides and monochlorides. Numerical Hartree–Fock (NHF) calculations are performed on selected systems to ensure that the extended Slater basis sets employed are near the Hartree–Fock limit. Because the bonding is predominantly electrostatic in origin, there is a strong correlation between the dissociation energy (to ions) and re. By dissociating to the ionic limits, most of the differential correlation effects can be embedded in the accurate experimental electron affinities and ionization potentials. With this model, correlation effects are relatively small (0.0–0.4 eV), but invariably increase D0. The importance of correlating the electrons on both the anion and the metal is discussed. For the heavier alkali chlorides, RbCl and CsCl, we show that a core‐valence treatment, which excludes the double excitations out of the metal (n−1) shell, gives significantly better re and D0 parameters than does the full singles plus doubles configuration‐interaction CI(SD) calculation. The theoretical studies combined with the experimental literature allow us to recommend D0 values that are accurate to 0.1 eV for all systems considered.