使用第一原理精確計算Ar-CF4及CF4-CF4分子間勢能函數

Accurate ab Initio Intermolecular Potentials for Ar-CF4 and CF4-CF4

陳嬿羽(Yan-Yu Chen)

指導教授 ： 張榮語

國立清華大學/工學院/化學工程學系/碩士(2010年)

摘要

本論文的目的是探討使用不同的量子化學計算方法及不同的基底函數，比較計算分子間勢能的精確度。本篇論文使用的計算方法為MP2及CCSD(T)，基底函數使用aug-cc-pVXZ (X= D, T, Q)，其中最重要的是將計算加入Bond Function，比較有加入及沒加入Bond Function的計算結果，以證明使用Bond Function不僅能在較低的理論層級或較少的基底函數下仍可得到精準的計算結果，並且節省大量的時間。在計算的分子為氬與四氟化碳的分子間勢能的結果可驗證我們所要證明使用Bond Function可提升計算品質及減少計算時間。因此在計算四氟化碳與四氟化碳的分子間勢能時加入Bond Function。

在開始計算前，首先要先建立分子的結構，並改變分子間距離來進行計算。使用GAUSSIAN03計算得到結果並整理完後，再將計算所得到的數據與Buckingham Potential進行擬合，找出勢能參數，方可將使用量子化學計算結果應用在分子動力模擬。其中我們使用C++撰寫一個使用將非線性轉線性的方法來尋找適合的參數的程式，並且使用基因演算法優化先前的方法所找到的勢能參數。

關鍵字

第一原理 ； 分子間勢能 ； 基因演算法 ； 虛擬粒子 ； 勢能參數 ； 基底函數

並列摘要

The purpose of this research is to investigate the accuracy of the intermolecular potential energies, which were calculated with different quantum chemistry methods and basis sets. The quantum chemistry methods that were used in this research are MP2 and CCSD(T), and the basis sets are aug-cc-pVXZ (X= D, T, Q). The most important part of the calculating methods is to add bond function in the calculations, and therefore by comparing the results between calculations with and without bond function, this research proved that with the use of bond function in the calculation, we can improve the calculating results. In other words, even if we used lower theory levels or decreased the number of basis sets in the calculations, we can still acquire accurate results, and therefore save a large amount of time. By calculating the intermolecular potentials between argon and CF4, we may confirm the advantages of the use of bond function we have mentioned above. Hence, the bond function is also added when calculating the intermolecular potentials between CF4 and CF4.

Before the calculation started, the orientations of the molecules need to be built. Then, we calculated the intermolecular potential energies with different distances between molecules. The software we use to do the calculation is GAUSSIAN03. The results, which were based on different quantum chemistry methods and basis sets, were then compared and discussed. The calculated results were fitted with Buckingham Potential and the parameters of the Buckingham Potential were found by a program, which is built by C++ and based on an algorithm that is to transform a non-linear function into a linear one. The gene algorithm was used to improve the parameters we acquired by the previous program.

參考文獻

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