基於量子化學方法研究四氯化碳分子間位勢能及四氯化碳流體之分子動力學模擬

我們使用HF、MP2及DFT三種量子化學計算方法計算四氯化碳分子間作用力，HF主要計算排斥力的部分，MP2計算整體凡得瓦爾力，基底大小對於HF的影響不大，對於MP2卻有相反的結果。並比較基底加入BSSE修正前後的影響，接著使用exchange-correlation functional的80種配對組合來進行DFT的計算，並比較合種配對較為接近MP2之計算結果。在完成量子化學計算後，使用4 Sites Lennard-Jones potential Model來進行ab initio計算的擬合，並建構出力場，再將擬合參數帶入分子動力學來進行模擬，模擬四氯化碳流體之結構特性、動態性值以及擴散係數，並與實驗相互比較。而模擬之結果有相當的準確度，說明由以量子力學做為出發點的分子動力學模擬，其在實用性上有一定的可靠度。此外，還針對甲烷分子進行擴散係數的分子動力學模擬，以了解模擬原子數對於擴散係數的影響。最後則討論位勢能間參數的轉換關係，由於擬合參數的好壞在分子動力學的模擬上佔了極大的因素，因此可透過轉換方式來改善擬合的結果。

關鍵字

四氯化碳； Hartree-Fock(HF)近似法； Møller-Plesset(MP)微擾理論；密度泛函理論(DFT) ；徑向分佈函數(RDF) ；速度自相關函數(VAF) ；擴散係數；分子動力學模擬(MD) ； Gaussian 03套裝軟體

並列摘要

We have calculated the interaction potentials of Carbon Tetrachloride dimers using the Hatree-Fock (HF) Self-Consistent theory, the correlation-corrected second-order Møller-Plesset (MP2) perturbation theory and the density functional theory (DFT). The main of HF calculations yield repulsive potentials, the MP2 calculations yield totally van der Waals interactions. The basis set number will occur to large influence to the HF calculations but the opposite results to MP2 calculations. Also compare the basis set superposition error (BSSE) corrected and uncorrected results. At last, we use eighty species of exchange-correlation functional to perform DFT calculations and the compare the results of MP2. After complete the quantum chemistry calculations, we use 4 Sites Lennard-Jones potential Model to curve fitting with ab initio calculations. By the 4 Sites Model, we can get the parameters and construct a force field to pave a way for the next step of molecular dynamics simulations. To simulate the structure properties, the dynamics properties and the diffusion coefficient of liquid carbon tetrachloride, we perform NVT ensemble of molecular dynamics simulations. We compare the results with experiments from several references and the results are acceptable for us. These results demonstrate that quantum chemistry calculated intermolecular interaction is very well which can reproduce the molecular dynamics simulation results with good accurately. Besides, we also simulate the diffusion coefficient of liquid methane to understanding the effect of the number of atoms of diffusion coefficient. Finally, we discuss the relationship of parameter between two different potentials. For the most part, the fitting results control the key point of molecular dynamics simulation results, so we can improve the fitting results by using the way of parameters transformation.

並列關鍵字

Carbon Tetrachloride ； Hatree-Fock (HF) approximation ； Møller-Plesset (MP) perturbation theory ； Density Function Theory (DFT) ； Radial distribution function (RDF) ； Velocity autocorrelation function (VAF) ； Diffusion coefficient ； Molecular Dynamics Simulations ； Gaussian 03 package

參考文獻

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基於量子化學方法研究四氯化碳分子間位勢能及四氯化碳流體之分子動力學模擬

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