Advanced ab initio and hybrid density functional theory evaluation of the atomization energies, bond dissociation pathways, and heats of formation of the two isomers of HClO 4

Abstract

The reliability of various ab initio and density functional theory models has been evaluated in the past for the study of bond dissociation energies, heats of formation, etc [1–3]. We present two novel results, the first being evidence for the formation of HO 4Cl, the first isomer, as well as the effect of basis set choice for a molecular orbital calculation of these types of systems. For all the density functional theory methods we have employed the B3LYP method with the 6-311++G (d, p), 6-311++G (2d, 2p), 6-311++G (3d, 3p), and 6-311++G (3df, 3pd) basis sets and have found that the predicted energies yield a higher energy for the second isomer of HClO 4, HOClO 3, but when a very large basis set was used (6-311++G (3df, 3pd)) the latter was found to be lower in energy than the former, which is in correlation with previously published results [1]. The same unusual effect were seen in the Hartree–Fock (HF), MP2, and MP4 methods where the 6-31G(d), 6-31G(d′), and 6-311G(d, p) were unable to correlate (to a reasonable extent for MP2 and MP4 methods) with the experimental value of around 4 kcal/mol for the heat of formation of HOClO 3 unless the CBSB3 or CBSB4 basis sets were implemented. We have also investigated five possible dissociation channels for radical mechanisms as well as the atomization energies of the two isomers at various theory methods, with various basis sets.