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  • 學位論文

乙醇在Pt(111)表面上的解離反應與推拉電子基分子系統的分子動態模擬之電子轉移理論研究

Theoretical study of ethanol decomposition on Pt(111) surface and electron transfer in push-pull molecular systems from ab initio molecular dynamics.

指導教授 : 林志興

摘要


論文提要內容: 在本論文的第一部分中,我們利用了以第一原理密度泛函理論(DFT)為基礎的CASTEP計算,搭配上ultrasoft pseudopotenital以及GGSA層級的使用,探討乙醇在Pt(111)-3x3金屬表面上的第一步O-H解離反應,和第二步經由四環方式與五環方式的C-H解離反應(Hydrogen elimination)。我們透過了部分結構限制法得到了第一步O-H解離反應的活化能為0.849eV,這與一般理論計算上的結果相符;在第二步的C-H解離反應中,經由四環方式的C-H解離反應活化能為0.319eV,而經由五環方式的C-H解離反應活化能為0.966eV,代表著第二步的C-H解離反應是以四環方式來進行,與實驗上所觀察到的結果一致,同時也與實驗上的反應溫度180K~240K相符。此外,藉由Pt-Pt鍵的結構變化來看,可以知道經由四環方式的結構變化就相對的比經由五環方式的來得小,說明了反應活化能的高低。最後,進一步的從電子結構態密度分析(DOS)得知,經由四環方式的C-H解離反應在過渡態時,其H與Pt會生成鍵結,同時在C=O上也會有π鍵生成,以降低活化能;此外,在與Pt接觸的C原子上,其混成軌域並無明顯的改變,說明了經由四環方式的C-H解離反應不需額外的能量付出。 在第二部分中,我們以SIESTA進行了CN-CH=CH-NH2、NO2-CH=CH-NH2與BH2-CH=CH-NH2¬這三個推拉電子基分子系統的第一原理分子動態模擬,並且蒐集了3ps下的電偶極矩、結構以及電荷的動態資訊。我們將電偶極矩的自動相關函數透過傅立葉轉換後,模擬出紅外線振動光譜,並搭配著PaDAF與SCAF的光譜解析方案成功的分析出分子中特徵官能基振動頻率,並與FTIR實驗的結果相近。同時利用了電荷自動相關函數透過傅立葉轉換後所得到的FT[charge-ACF]光譜,與紅外線振動光譜比對,建立了電荷轉移與分子運動的關聯性,並且指出造成電荷轉移的特定官能基運動模式。此外,透過了推電子基與拉電子基的電荷動態觀察,我們根據電荷的震盪程度大小估算出電荷轉移的速率,說明這三個分子的電荷轉移效應。最後,我們針對了CN-CH=CH-NH2的系統做了溫度效應的探討,同時計算出分子的熱誘導電荷轉移的活化能大小。

並列摘要


Abstract: In part 1 , total energy calculation based on Density Function Theory (DFT) with Ultrasoft-pseudopotenital and generalized gradient spin-polarized approximation (GGSA) was used to investigate (1) O-H cleavage of ethanol and (2)C-H hydrogen elimination via four-membered ring and five-membered ring on Pt(111)-3x3 surface. By means of Partial Structure Constrain Path Minimization(PSCPM) method , our calculated energy barrier for O-H cleavage is 0.849eV and C-H hydrogen elimination via four-membered ring and five-membered ring are 0.319eV and 0.966eV , respectively. These results are in good agreement with TPD experimental result. Furthermore , we found that (1) less change in Pt-Pt dimmer bond length and (2) more H-Pt bond formation , less change in carbon hybrid orbital and π bonding in C=O by means of the partial density of state (PDOS) for the four-membered-ring hydrogen elimination to explain reaction selectivity. In part 2 , we performed first principle molecular dynamics based on Density Function Theory with norm-conversing pseudopotential and accurate LCAO basis set in SIESTA package on CN-CH=CH-NH2 , NO2-CH=CH-NH2 and BH2-CH=CH-NH2¬ push-pull molecule system and we collected dipole moment ,structure and charge trajectory in 3ps molecular dynamics. We used Fourier Transformed dipole moment AutoCorrelation Function to simulate IR spectra and analyzed characteristic vibration mode in molecule by using PaDAF and SCAF method. By comparison of Fourier Transformed charge AutoCorrelation Function (FT[charge-ACF]) and IR spectra , we found that main-chain vibration mode induced charge transfer. Furthermore , we calculated charge transfer rate by utilizing charge dynamics and explain charge transfer effect of these push-pull molecules.Finally , we also investigated temperature effect on charge transfer and calculated activation barrier of charge transfer.

參考文獻


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被引用紀錄


巫昶昕(2009)。以理論計算方法探討乙醇和甲醇在nNi/gamma-Al2O3(110)(n=1,2)表面的脫氫反應〔碩士論文,國立臺灣師範大學〕。華藝線上圖書館。https://www.airitilibrary.com/Article/Detail?DocID=U0021-1610201315154995

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