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Finitetemperature density functional approach to electrochemical reaction
https://ir.soken.ac.jp/records/252
https://ir.soken.ac.jp/records/25229725b930a36479c817ef4922e1d7e3d
名前 / ファイル  ライセンス  アクション 

要旨・審査要旨 (387.7 kB)

Item type  学位論文 / Thesis or Dissertation(1)  

公開日  20100222  
タイトル  
タイトル  Finitetemperature density functional approach to electrochemical reaction  
タイトル  
タイトル  Finitetemperature density functional approach to electrochemical reaction  
言語  en  
言語  
言語  eng  
資源タイプ  
資源タイプ識別子  http://purl.org/coar/resource_type/c_46ec  
資源タイプ  thesis  
著者名 
白鳥, 和矢
× 白鳥, 和矢 

フリガナ 
シラトリ, カズヤ
× シラトリ, カズヤ 

著者 
SHIRATORI, Kazuya
× SHIRATORI, Kazuya 

学位授与機関  
学位授与機関名  総合研究大学院大学  
学位名  
学位名  博士（理学）  
学位記番号  
内容記述タイプ  Other  
内容記述  総研大甲第1117号  
研究科  
値  物理科学研究科  
専攻  
値  07 構造分子科学専攻  
学位授与年月日  
学位授与年月日  20080319  
学位授与年度  
値  2007  
要旨  
内容記述タイプ  Other  
内容記述  Electrochemical processes have historically been investigated in a wide range of<br> interests in electrochemical cell, corrosion, membrane potential and analytical<br> technique. Their importance has extensively been recognized in recent years, for<br> example, in the context of energy conversion related to photoelectrochemical cells<br />based on advanced fabrication technology. To analyze these electrochemical processes,<br />it is required to clarify electronic structures of a system in electrochemical<br> environment. Nevertheless, it is computationally demanding to carry out<br />firstprinciples calculations of such electronic states. This is simply because<br />reactantsolvent and reactantelectrode interactions, which are completely absent in<br />isolated molecular systems, play an important role. Therefore, the electrochemical<br> processes have so far been studied within various numerical models at different levels<br />of theory. The problems in the electrochemical processes can be classified into two<br />parts. The first problem is difficulty in carrying out electronic structure calculations of<br />the reactant molecule at a constant chemical potential µ, and the other one is how to<br />appropriately describe the reactantsolvent and the reactantelectrode interactions. <br /> The conventional <i>ab initio</i> calculations are directed toward obtaining electronic<br />structures at a constant number of electrons, <i>N</i> . Such <i>ab initio</i> calculations cannot be<br />straightforwardly applied to electronic structure calculations at a constant µ, in <br />which the number of electrons is not a suitable variable. Although several studies have<br />been devoted to development of the methods calculating electronic structures at a<br />constant µ, their methods are still substantially based on the constant <i>N</i><br />calculations. Therefore, it is desirable to develop an alternative method to directly<br />calculate electronic structures at a constant µ. Finitetemperature density functional<br />theory (FTDFT) treats a system in a grand canonical ensemble average and thus one<br />can propose a numerical method based on FTDFT to describe electrochemical<br />processes. <br /> In addition to the requirement for the electronic structure calculation at a constant<br />µ, reactantsolvent and reactantelectrode interactions should be considered in <br />electrochemical processes, as mentioned above. He primarily focuses on developing the FTDFT method of electronic structure calculation of reactant molecules at a constant<br />µ. Therefore, he approximates the solvent effects in terms of a simple continuum<br />model and limit electrochemical processes to outersphere ones in which the electrode<br />is treated as a reservoir with µ. It should be noted that the development of the<br />electronic structure calculation has nothing to do with the treatment of the<br />reactantsolvent interaction, so that the present FTDFT method can be<br />straightforwardly improved by employing more sophisticated procedures describing<br />the solvent effects. <br /> In this thesis, he develops a method of the FTDFT ab initio quantum chemistry<br />calculations combined with a continuum solvent model and discuss the electronic<br />properties of molecules in electrochemical environment. The actual calculations are<br />carried out by solving the finitetemperature KohnSham (KS) equation with the<br />GAMESS package of quantum chemistry programs in which the present numerical<br />methodology of FTDFT is implemented. The KS orbitals are expanded in terms of<br />Dunning's augmented correlationconsistent basis set (augccpVDZ). <br /> He applies the present method to the electrochemical reaction,NO<sup>+</sup>+e<sup></sup>↔ NO . The <br />Becke threeparameter hybrid exchange functional with the LeeYangParr correlation <br />functional (B3LYP) is used as the exchangecorrelation potential. He does not<br />consider the temperature dependence of the exchangecorrelation potential although<br />the potential in the FTDFT approach should depend on temperature in a narrow sense.<br />The solvent effects are treated at the level of conductorlike polarizable continuum<br />model (CPCM), assuming the equilibrium condition between the solute and the<br />solvent. He gives the size of the cavity in CPCM as a function of the molecular charge.<br />The calculation is carried out at the chemical potentials µ 3.40, 5.40, and 7.40 eV.<br />These values correspond to the electrode potentials <i>v</i> = 0.84, 1.16, and 3.16 V vs<br />SHE (standard hydrogen electrode), respectively. It has successfully been<br />demonstrated that the grand potential curve depends on µ, i.e., the electrode <br />potential. The calculation showed that the charge is a function of the chemical <br />otential and the internuclear distance of NO. The FTDFT/CPCM approach has<br />proved to be a useful computational tool for electronic structure calculations at a<br />constant µ of a molecule interacting with solvent molecules.<br /> Although the FTDFT/CPCM method has succeeded in giving the reasonable results,<br />there are two problems to be addressed: the B3LYP functional is used uncritically and<br />the nonequilibrium solvation effect is not taken into account. These unsettled <br />problems might give rise to serious disadvantages in analysis of electrochemical<br />kinetics. Thus, he improves the FTDFT approach further by employing a different<br />functional and a different continuum solvent model, as mentioned bellow. This <br />improved FTDFT method is also applied to the electrochemical reaction<br />of NO<sup>+</sup>+e<sup></sup>↔NO. <br /> In the extension of the HohenbergKohn theorem to the system with a fractional<br />number of electrons <i>N</i> by Perdew <i>et al</i>., they demonstrated that the energy<br />calculated by using DFT should show derivative discontinuity with respect to <i>N</i> .<br />However, it is known that the B3LYP functional does not reproduce the derivative<br />discontinuity condition. He alternatively employs the Becke exchange and<br />LeeYangParr correlation functional with a longrange correction (LCBLYP). The<br />result obtained by using the LCBLYP functional depends on the parameter ω that<br />divides the Coulomb operator into shortrange and longrange parts. It has been found<br />that the B3LYP functional completely fails to describe the grand potential surface<br />whereas the LCBLYP functional gives a proper grand potential surface if an<br />appropriate value of ω is taken. This is because the result of the LCBLYP functional<br />with the optimal value of ω satisfies the requirement of the derivative discontinuity<br />with respect to <i>N</i>. <br /> To treat the nonequilibrium solvation effect, he uses the extended selfconsistent<br />reaction field (SCRF) model. This model allows considering the nonequilibrium<br />solvation effect by dividing solvent polarization into longlived and shortlived<br />components. The calculated activation free energy, 12 kcal/mol, was in good agreement<br />with an experimental result, 11 kcal/mol, whereas the result obtained by using the<br />conventional SCRF model (i.e., not taking account of the nonequilibrium solvation<br />effect) gave considerably lower value, 3 kcal/mol. He has clearly shown that the<br />nonequilibrium solvation effect has a great influence on the electrochemical process<br />and the extended SCRF model significantly improves the calculated activation free<br />energy.<br /> In summary, he has developed a computational method based on FTDFT combined<br />with a continuum solvent model to analyze electrochemical processes. The FTDFT<br />method allows calculating the electronic structures as a function of the chemical <br />potential. To apply the method to the studies of electrochemical kinetics, use of a<br />nonequilibrium solvation model and an exchangecorrelation potential satisfying the <br />derivative discontinuity is crucially important. This study provides a powerful and <br />intuitive approach to analysis of electrochemical reactions.<br />  
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