The role of core–valence electron correlation in gallium halides: a comparison of composite methods

Abstract

The electronic structure and atomization energies of gas phase gallium halides (GaXn where X = F, Cl, Br, and I, and n = 1 … 3) are studied with highly accurate ab initio composite methods. Coupled cluster methodologies up to full hextuples (CCSDTQPH) are used to compute spectroscopic properties of GaF, which are compared with experiment and conventional levels of theory [such as complete basis set CCSD(T)]. An appropriate treatment of core–valence electron correlation is necessary to obtain reasonable geometries and atomization energies. More efficient composite methods such as the correlation consistent Composite Approach (ccCA, ccCA-TM, rp-ccCA) and the Gaussian-n methods [G3, G3(MP2), G4, G4(MP2)] are calibrated to explore application toward large GaXn-containing molecules relevant to catalysis. For the 12 GaXn compounds, ccCA-TM and rp-ccCA with Boys-localized molecular orbitals has a mean absolute deviation of 1.41 kcal mol−1 compared to complete basis set CCSD(T). However, the G3(MP2) method performs better for complexes with the lighter halides. Calibration of GaXn (X = F, Cl, Br, and I; n = 1–3) ab initio atomization energies is useful to improve prediction of ligand binding energies in novel gallium halide-containing catalysts. Inorganic and organometallic complexes with GaXn ligands are extremely difficult to synthesize and characterize. Therefore, rational design based on well-understood theory is essential.