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Abstract: The effect of constraints on the initial steps of the incorporation of nitrogen on silicon has been assessed by calculations with the [Si9H12 +N] model cluster using density functional theory with the hybrid functional B3LYP, and two basis sets that differ significantly in size. The relative stability of the various stationary points is dependent on the type of constraints imposed on the cluster. Constrained calculations have predicted the structure with the nitrogen symmetrically bonded to the dimer silicons as the global minimum, however, if no constraint is imposed and the whole cluster is optimized, as done in this work, a structure with the nitrogen inserted between the dimer and the first layer and bonded to three silicon atoms is predicted to be the most stable one by about 17kcal/mol by either the doublet or quartet route. The whole process is very exothermic and reaction barriers in the intermediate steps are easily overcome. Calculations with the smaller basis do not essentially change the major conclusion about the relative stability of the various stationary points. The most stable structure and frequency calculations are consistent with a planar NSi3 moiety and its asymmetrical stretching frequency. [Copyright &y& Elsevier]

Abstract: A theoretical study of the electronic structure of zinc phthalocyanine (ZnPc) ground state was carried out using ab initio and DFT methods. The DFT and MP2 methods indicated a D 4h structure, while HF predicted a slightly distorted geometry. The DFT infrared spectra with the corrected wave number values presented good agreement with experiment. The solvation influence on the geometrical parameters, atomic charges and HOMO–LUMO energies was estimated with the use of PCM method and DMSO as solvent. The presence of solvent did not alter these parameters, but affected the orbital energies. The aggregation phenomena were studied with ZnPc dimer and trimer structures. The previously unknown ZnPc dimer infrared spectrum was obtained and compared to the one from monomer. The dimer and trimer stabilization energies are indicative that the formation of stacked structures with several ZnPc is a favorable process. [Copyright &y& Elsevier]

Abstract: Barrier heights, structures, reaction energies, and rate constants are calculated with the DFT, MP2, and CCSD(T) methods for the first two channels of the H+CH3OH reactions. The best estimate results based on CCSD(T) calculations give reaction enthalpies () for the first (−8.4kcal/mol) and second (0.8kcal/mol) reactive channels, which are comparable to the experimental values, −8.8±0.9 and −0.3±0.9kcal/mol, respectively. Rate constants and activation energies calculated with the IVTST-0 method using CCSD(T)/cc-pVTZ geometries and frequencies are also in excellent agreement with experiment data. [Copyright &y& Elsevier]

Abstract: Thermochemical and kinetics properties of the hydrogen abstraction and addition processes of the reaction were computed using high-level ab initio and DFT approximation methods with aug-cc-pVXZ (X=T,Q) basis set. The CCSD (T)/CBS//BB1K/aug-cc-pVTZ results for classical barrier height are 13.1 and 15.0kcal/mol for the abstraction and addition reactions, respectively. The thermal rate constants were calculated using the dual-level direct dynamics by variational transition state theory with the BB1K potential energy surface and thermochemical properties corrected with the CCSD (T)/CBS//BB1K/aug-cc-pVTZ results. The rate constants calculated show that the variational and tunneling effects play a relevant role only for the abstraction reaction. [Copyright &y& Elsevier]