Molecular Dynamics Simulations of Methane Fluids using Quantum Chemistry Calculated Intermolecular Interactions
Date Issued
2007
Date
2007
Author(s)
Ching-Cheng, Pai
DOI
zh-TW
Abstract
We have calculated the intermolecular interaction potentials of the methane dimer at the minimum-energy D3d conformation using the Hartree-Fock (HF) self-consistent theory, the correlation-corrected second-order Møller-Plesset (MP2) perturbation theory and the density functional theory (DFT). The HF calculations yield unbound potentials largely due to the exchange-repulsion interaction. In the MP2 calculations, the basis set effects on the repulsion exponent, the equilibrium bond length, the binding energy, and the asymptotic behavior of the calculated intermolecular potentials have been thoroughly studied. Up to the largest basis set used, the asymptotic dispersion coefficient has not converged to the destined C6 value from molecular polarizability calculations. The slow convergence could indicate the inefficacy of using the MP2 calculations with Gaussian-type functions to model the asymptotic behavior. Both the basis set superposition error (BSSE) corrected and uncorrected results are presented to emphasize the importance of including such corrections. Only the BSSE corrected results systematically converge to the destined potential curve with increasing basis size. The DFT calculations generate a wide range of interaction patterns, and compare with MP2 results.
Next, we use a curve fitting method to fit the results of quantum chemistry calculation. We can get the force parameters of bond lengths and binding energies and then input them to solve Newton’s equations. To simulate the equilibrium properties and dynamics properties of methane liquid, we perform NVT ensemble molecular dynamics simulations. Our results well reproduce the experimental data. It demonstrates that quantum chemistry calculated intermolecular interaction is very good. Beside we simulate the equilibrium properties and dynamics properties along the vapor-liquid curve and solid-liquid curve in the phase diagram using three potential models.
Subjects
Hartree-Fock (HF) 近似法
Mø
ller-Plesset (MP) 微擾理論
密度泛函理論 (DFT)
徑向分布函數 (RDF)
速度自相關函數 (VAF)
擴散係數
Gaussian 03 套裝軟體
Hartree-Fock (HF) approximation
ller-Plesset (MP) perturbation theory
Density functional theory (DFT)
Radial distribution function (RDF)
Velocity autocorrelation function (VAF)
Diffusion coefficient
Gaussian 03 package
Type
thesis
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