The effect of basis set superposition error ͑BSSE͒ on Gaussian-2 and Gaussian-3 calculated alkali metal cation-ligand affinities has been studied. For these systems, we found that the standard Boys-Bernadi full counterpoise ͑CP͒ method often leads to correction terms that are physically incorrect. This problem may be rectified by using the geometry corrected counterpoise ͑GCP͒ method. The relationship between CP, GCP corrections, and deformation energy is discussed. In order to yield good agreement with existing experimental Li ϩ and Na ϩ ligand affinities, we recommend the adoption of either the G3 ͑with GCP correction͒ or the G2͑MP2,SVP͒-FC ͑without GCP correction͒ protocols. In the case of K ϩ , the GCP correction is of negligible magnitude, and hence GCP corrections may be omitted in the G2͑MP2,SVP͒-ASC affinity calculations for these complexes.

A high-level theoretical study on the thermochemistry of hydrochlorofluorosilanes has been carried out using the Gaussian-3 (G3), and its computationally less expensive variant G3(MP2), methods. In this paper, we report the heats of formation of 15 silanes, their adiabatic ionization energies (IEs), electron affinities (EAs), and proton affinities (PAs), as well as the acidities of 10 hydrosilanes. Good to excellent agreement with the available experimental data is found for essentially all calculated quantities. The only exceptions are those involving the SiF 4 + cation, such as the IE and PA of SF 4 . The origin of this failure is not immediately clear, even though this failure is not confined to the G3 methods. Because many of the thermochemical data for the industrially important silanes are not available in the literature, the results reported here may be taken as reliable estimates.

Using density functional theory, we predicted the solution structure of the hydrolyzed 3–aminopropyltriethoxysilane (h–APS), which is a silane coupling agent commonly used in many industrial applications. We have located five stable minima on the potential energy surface of h–APS in which four of them are "neutral", and the remaining one is zwitterionic (dipolar) in nature. Our calculations suggested that the stability of the most stable form of h–APS in water (denoted as II_N) arose from strong intramolecular OH ⋯ N hydrogen bond. The least stable form is the zwitterionic form (I_ZW), which is estimated to be over 90 kJ mol -1 less stable than II_N. The factors governing the relative stabilities of different forms are discussed.