| Summary: | 博士 === 臺灣大學 === 應用力學研究所 === 98 === In this study, intermolecular interaction energy data for the tetrahedral molecule dimers have been calculated at a spectroscopic accuracy and employed to construct an ab initio potential energy surface (PES) for molecular dynamics (MD) simulations of tetrahedral molecule properties. The full potential curves of the tetrahedral molecule dimers at 12 symmetric conformations were calculated by the supermolecule counterpoise-corrected Hartree-Fock (HF), Density Function Theory (DFT), second-order Møller-Plesset (MP2) perturbation theory and single-point coupled cluster with single and double and perturbative triple excitations [CCSD(T)] calculations were also carried out to calibrate the MP2 potentials. We employed Pople’s medium size basis sets [up to 6-311++G (3df, 3pd)] and Dunning’s correlation consistent basis sets (cc-pVXZ and aug-cc-pVXZ, X = D, T, Q, 5). For each conformer, the intermolecular carbon–carbon separation was sampled in a step 0.1 Å for a range of 3.0 ~ 9.0 Å. The MP2 binding curves display significant anisotropy with respect to the relative orientations of the dimer. The potential curves at the complete basis set (CBS) limit were estimated using well-established analytical extrapolation schemes and while a large basis set (aug-cc-pVTZ) is required to converge the binding energy at a chemical accuracy (~0.03 kcal/mol). A 4-site and 5-site potential models were used to fit the ab initio potential data. We performed molecular dynamics simulations using the ab initio force field and compared the simulation results to experiments. Quantitative agreements for the atomwise radial distribution functions, the self-diffusion coefficients, and the X-ray and Neutron diffraction scattering functions over a wide range of experimental conditions can be obtained, thus validating the ab initio force field without using experimental data a priori.
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