利用密度泛函理論研究一氧化碳過渡金屬表面上的吸附

Density Functional Study of CO Adsorption on Transition Metals

王柏翔(Po-Shiang Wang)

指導教授 ： 李錫隆

國立中正大學/理學院/化學暨生物化學系/碩士(2015年)

摘要

在此研究中，我們使用密度泛函理論來研究過渡金屬表面和一氧化碳之間的作用力。我們研究CO吸附在其他過渡金屬的”CO/M9-9-8(111) puzzle”，進而使用了四種DFT 計算方法，分別是B3LYP, BMK, M06-2X 和M06-HF 用這些計算方法去重新驗證 CO 吸附在Au（111）, Ag（111）, Cu（111）, Ir（111）, Pd（111）, Pt（111）,和 Rh（111）表面，並且利用化學鍵結分析來探討不同函數對吸附行為預測的差異。
　　在本次實驗中, 結果顯示利用B3LYP, BMK, M06-2X 和M06-HF 方法我們可以對於CO 吸附在Ag(111),Ir(111) 和Pt(111)表面上可以預測出與實驗相符的吸附位相。 對於其他金屬來說預測的吸附位相或是吸附能不一定跟實驗值相符合。 我們發現M06-2X計算出來的平均誤差和平均絕對誤差與其他方法相比是比較小的，但是對於大部分的金屬而言M06-2X在預測吸附位相中是預測不準的。
　　在過去我們實驗室黃郁偉學長的研究中指出當HF交換能的項增加可以改善CO LUMO位置，但是這項改善不足夠用於預測CO的吸附位向，以解決 CO/M puzzle 的問題。因此我們用Blyholder等人提出的鍵結模型，畫出各個金屬的DOS圖想要去了解當HF交換能的項增加對金屬的影響，結果顯示當HF交換能的項增加，過渡金屬的能帶間隙會增加使得金屬變得比較沒有金屬的性質。因此當HF交換能的項增加能改善CO 的LUMO能量算的同時但是金屬的部分是算的越來越糟，導致HF交換能的項增加並不能使得CO的吸附性質與實驗值更加相符合。由於這個Blyholder鍵結模型還不足以解釋CO 的吸附位向的問題，只能解釋各個方法預測CO和金屬間吸附的不同作用力大小我們進而用了Dimakis 等人提出的鍵結模型來對CO與各個金屬間的鍵結更加詳細的鍵結分析。

關鍵字

一氧化碳吸附 ； 密度泛函理論 ； 過渡金屬

並列摘要

In this work, the density functional theory was applied to study the interactions between carbon monoxide (CO) and transition metal M9-9-8 (M=Ag, Au, Cu, Pd, Pt, and Rh) clusters mimicking (111) surfaces. The CO/ M9-9-8 (111) puzzle was examined by using the hybrid B3LYP, hyper BMK, M06-2X and M06-HF functionals. The chemical bonding analysis was also considered to check the difference between functionals in predicting the adsorption behavior. The results show that hybrid B3LYP, hyper BMK, M06-2X and M06-HF methods give good adsorption site preferences for CO adsorption at Ag(111), Ir(111) and Pt (111) surfaces compared to experimental results. For other transition metals, the methods failed to provide adsorption preferences or adsorption energies compared to experimental results. The results also show that M06-2X method gives smaller mean absolute deviation and smallest mean deviation, but it also fail to predict correct adsorption site for most of the transition metals.
　　In the previous work, Huang et al. proposed when adding more contribution of HF exchange in functional, leading to the raising of the CO LUMO energy, but the improvement is not enough to solve the CO/M puzzle. Therefore, the density of states (DOS) of seven transition metals figure by using Blyholder bonding model. The results show when adding more contribution of HF exchange in functional, CO LUMO get better description but for transition metals become less metallic properties. Therefore, better description of CO LUMO still is not enough via adding more contribution of HF exchange in functional solve CO/M puzzle an electronic structures of descriptions of the metal clusters are getting worse.
In addition, to further understand the CO and transition metal adsorption preferences, the Dimakis bonding model also applied to investigate the site preference calculated by B3LYP method.

並列關鍵字

CO adsorption ； Density Functional Theory ； Transition metals

參考文獻

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