- 學位論文
環丙烷分子之量子化學勢能計算與分子動力學模擬
Quantum Chemistry Calculated Intermolecular Interaction and Molecular Dynamics Simulation of Cyclopropane
摘要
在量子計算的部份，我們使用經過BSSE(Basis Set Superposition Errors)修正的自洽理論 (Hartee-Fock Approximation，HF)、微擾理論(M?ller-Plesset Perturbation Theory，MP2)、密度泛函理論(Density Functional Theory，DFT)及偶合簇理論(Coupled Cluster Method)等四種量子力學理論來計算環丙烷的分子間作用力，其中使用MP2方法搭配從6-31(G)到aug-cc-PVXZ(X=D、T、Q)的基底來計算環丙烷的最佳化構型，並與CCSD(T)搭配aug-cc-PVXZ(X=D、T)基底所計算出的基底極限能量比較，接著加入數種DFT方法且搭配一系列基底並將結果與CCSD(T)所算出的參考值比較，幫助我們找出更節省計算資源的方法。再來我們選取環丙烷二聚體有可能形成的15種構型(A~O)，以 HF計算其排斥力、靜電力及感應電磁力，並用MP2/aug-cc-pVTZ計算出完整位勢能曲線後配合PSI4軟體中的SAPT方法分解出靜電能、誘導能、交換能與色散能，以更進一步分析分子間作用力的排斥力及吸引力對環丙烷二聚體的穩定性影響。 在完成量子化學計算後，我們使用9site model與Lennard-Jones potential來擬合由量子化學計算得到的環丙烷分子二聚體位能曲線，並建構出力場，接著將其代入牛頓方程式進行分子動力學模擬，藉以得到環丙烷的平衡性質及動態性質，並與實驗值以及現有的文獻比較。我們對環丙烷的模擬我們從三相點沿著氣化曲線計算至臨界點，模擬了不同溫度與密度下的徑向分佈函數(Radial Distribution Function，RDF)、速度自相關函數(Velocity Autocorrelation Function，VAF)、擴散係數(Diffusion constant)及剪力黏滯係數(Shear Viscosity)，皆有相當不錯的準確度，這說明了以量子化學計算出的勢能曲線所建構出的力場來進行分子動力學模擬在實用性上亦有一定的可靠度。
並列摘要
The first topic of this research is quantum chemistry calculation to cyclopropane. We have calculated the intermolecular interaction energy of the cyclopropane dimer with Hatree-Fock self-consistent theory(HF), second-order M?ller-Plesset perturbation theory(MP2), density functional theory(DFT) and coupled cluster(CC) method, and the correction of the basis-set superposition error(BSSE) has been included. In the structure optimization and binding energy calculations of cyclopropane, we employed MP2 method with Pople’s series basis sets (6-31(G) up to 6-311++G(3df,3pd)) and Dunning’s correlation consistent basis sets(cc-pVXZ (X=D、T)and aug-cc-pVXZ, (X=D、T、Q). In addition, single-point coupled cluster with single and double and perturbative triple excitation (CCSD(T)) calculations were carried out to calibrate the MP2’s binding energy. For 15 cyclopropane conformers, the HF calculation yields repulsion, electrostatics and induction energies, and the MP2 calculation shows full potential curves. In the other hand, PSI4 software was utilized through SAPT method to decompose the intermolecular interaction into four parts, as electrostatic energy、 induction energy、 dispersion energy、 exchange energy, to analyze the repulsion and attraction effect on stability of cyclopropane dimer. After the quantum chemistry calculation is completed, we choose 9site model with Lennard-Jones potential to fit the ab initio data, and construct the force field by the parameters we found. Then perform the molecular dynamics simulation from cyclopropane’s triple point to the critical point along the gasification curve with different temperatures and corresponding densities. In addition, we compare the equilibrium and dynamic properties with the experiment data and previous investigations. The comparison of the radial distribution function (RDF), velocity autocorrelation function (VAF), diffusion constant and shear viscosity is acceptable. It shows that using the result of quantum chemistry computation to construct the force field can accurately reproduce the thermal properties.