Ab initio all-electron and effective core potential calculations on CuCl2?4

Abstract

Structural and energetic results are reported from a series of ab initio calculations on ground state CuCl in D2d and D4h conformations. All-electron Hartree–Fock calculations including geometry optimization have been carried out with large basis sets reaching triple-zeta valence plus f-function quality. Several ab initio effective core potentials and valence basis sets for Cu and Cl have been tested and evaluated based on comparisons of calculated results obtained at the Hartree–Fock or correlated (Moller–Plesset perturbation theory) levels with the all-electron and experimental data. The optimized structural parameters provided by all-electron or effective core potential methods are very similar, but they differ from averaged experimental data. Thus, the calculated CuCl bond lengths are typically 0.15–0.20 A too large, and the ClCuCl bond angle (D2d) is 10–15° too small. The square planar (D4h) conformation represents a transition state and not a structural minimum for CuCl. The energy difference between the two conformations (D4h – D2d) is consistently 16–18 kcal/mol at the Hartree–Fock level but approaches 10–12 kcal/mol at the highest levels of theory applied (UMP4(SDTQ)).