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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: The CH4 +F(2P)→CH3 +HF abstraction reaction was investigated using the BH&HLYP, MP2, and CCSD(T) approaches, and two series of correlation consistent basis sets. At the CCSD(T)/cc-pVTZ level, the classical barrier height (ΔV #), and the vibrationally adiabatic ground-state barrier height () are equal to 1.8 and 0.5kcal/mol, respectively. CCSD(T)/cc-pVQZ calculations give a value for the enthalpy of reaction at 0K () of −31.5kcal/mol (Expt. −32.1kcal/mol). Rate constants calculated with the zero-order interpolated variational transition state (IVTST-0) method are in agreement with experiment. The activation energy computed as local two-points slopes of Arrhenius plots in the temperature range of 200–400K, equal to 0.59kcal/mol, is also in good agreement with experiment (0.53kcal/mol). [Copyright &y& Elsevier]

Abstract: The lowest singlet and triplet states of AlP3, GaP3 and BP3 molecules with Cs, C2v and C3v symmetries were characterized using the B3LYP functional and the aug-cc-pVTZ and aug-cc-pVQZ correlated consistent basis sets. Geometrical parameters and vibrational frequencies were calculated and compared to existent experimental and theoretical data. Relative energies were obtained with single point CCSD(T) calculations using the aug-cc-pVTZ, aug-cc-pVQZ and aug-cc-pV5Z basis sets, and then extrapolating to the complete basis set (CBS) limit. [Copyright &y& Elsevier]