Bonding in the homologous series CsAu, CsAg, and CsCu studied at the 4-component density functional theory and coupled cluster levels

We have studied the effect of relativity, electron correlation and the lanthanide contraction on the spectroscopic constants, dissociation energies and dipole moments of the homologous series CsAu, CsAg, and CsCu. We observe a relativistic strengthening of the bond in all cases, particularly for CsAu, but all three compounds are predicted to exist on both the relativistic and nonrelativistic levels of theory with bond strengths more than 1 eV. The effect of the lanthanide contraction on the bonding in CsAu has been studied using a pseudoatom model of the Au atom and is shown to contribute to the strength and polarity of the bond, albeit to a lesser degree than relativity. We present a new estimate of the experimentally derived value of the CsAu dissociation energy using spectroscopic constants calculated at the coupled cluster CCSD(T) level. The new value (2.53 eV) is slightly lower than the previous estimate by Busse and Weil (2.58 eV) and is in excellent agreement with the corresponding CCSD(T) value. We have employed 4-component density functional theory at the B3LYP level, and the spectroscopic constants calculated with this method are in good agreement with coupled cluster results. For dipole moments the B3LYP values appear on the other hand to be too low and this requires further investigation. (C) 2003 American Institute of Physics.