Molecular Orbital Anaysis of Water Activation on TiO₂(110) Surface

강대복,강대복 Korean Chemical Society 2002 대한화학회지 Vol.46 No.3

A molecular orbital analysis based on the extended Huckel calculations has been carried out to study the OH bond activation of water on the $TiO_2$(110) surface. $H_2O$ binds with its axis perpendicular to the surfac on top of the five-coordinate $Ti^{4+}$ atom via its $3a_1$ orbital. In this bonding situation, the two-coordinated bridging $O^{2-}$ atom ($O_b$, basic site) on $TiO_2$(110) is too distant from an H atom of water to form hydrogen-bondig interactions with water that facilitate O-H bond cleavage. It has been elucidated that the O-H bond is appreciably weakened when the water molecule is tilted to give a hydrogen bond with the $O_b$ atom. This mechanism includes mutual transfer of electron density from the $3a_1$ orbital of the water molecule to the $Ti^{4+} 3d_{z2}$ orbital and from the $O_b$ P orbitals to the $2b_1$ of the adsorbed water molecule This should result in lengthening of the O-H bond in the surface complex and the subsequent dissociation into the fragments OH and H. $TiO_2$(110) 표면에서 물의 OH 결합 활성화가 어떤지 전자적 메카니즘에 의해 이루어지는 extended Hiickel 방법을 통해 알아보았다. 물분자는 $3a_1$오비탈의 시그마 상호작용 겨로가로 5배위 $Ti^{4+}$원자바로위에 수직으로 흡착한다. 이 결합구조에서는 물분자의 H원자가 $TiO_2$의 2배위 bridging $O^{2-}(O_b)$원자와 너무 멀리 떨어져 있으므로 OH 결합 해리를 촉진시키는 수소결합 상호 작용을 할 수 없으므로 물분자를 $O_b$ 원자쪽으로 기울여 수소결합이 형성되도록 한다. 이 경우 $O_b$ P 오비탈로부터 흡착 물분자의 LUMO $2b_1$반 결합성 오비탈로 전자밀도의 이동이 일어나고 또 물의 $3a_1$오비탈(약한 결합성)로부터 $Ti^{4+} 3d_{z2}$오비탈로 전자밀도의 이동이 일어남으로써 물의 OH 결합이 상당히 약화됨을 확인할 수 있었고 그 결과 OH와 H로 해리할 것이라는 해석이 가능하다.

Spin Exchange Coupling in Dimethoxo-Bridged Dichromium(III) Complexes: A Density Functional Theory Study

강대복 대한화학회 2008 Bulletin of the Korean Chemical Society Vol.29 No.5

For the [Cr₂(H₂tmp)₂Cl₄] compound, simplified models with two bridging methoxo ligands have been studied. The influence of the bridging Cr-O-Cr bond angles on the exchange coupling between metal atoms in the model compound has been analyzed by means of density functional calculations with the broken-symmetry approach. Coupling constant calculated for the full structure is in good agreement with the experimentally reported value, confirming the validity of the computational strategy used in this work to predict the exchange coupling in a family of related dinuclear Cr(III) compounds. The calculations indicate a good correlation between the calculated coupling constant and the sum of the squared energy gap of three pairs of metal t₂g OMSOs with a limited variation of the Cr-O-Cr angle. The spin density distribution and the mechanism of magnetic coupling interactions are discussed.

Influence of Different A Elements on Bonding and Elastic Properties of Zr2AC (A = Al, Si, P, S): A Theoretical Investigation

강대복 대한화학회 2013 Bulletin of the Korean Chemical Society Vol.34 No.2

Extended Hückel tight-binding band structure calculations are used to address the chemical bonding and elastic properties of Zr2AC (A=Al, Si, P, and S). Elastic properties are interpreted by analyzing the density of states and the crystal orbital overlap population for the respective phases. Our results show that the bulk modulus of these ternary compounds is determined by the strength of Zr-A bonds.

위점막내 점액질과 몇 가지 효소에 관한 비교조직화학적 연구

강대복 부산의대 1974 부산의대잡지 - 부산대학교 의과대학 Vol.14 No.1

Bonding at Fe(001)/TiC(001) Interface

강대복 대한화학회 2015 Bulletin of the Korean Chemical Society Vol.36 No.2

The bonding of the interface between bcc Fe(001) and TiC(001) is investigated by means of the extended Hückel tight-binding band structure calculations. Two different interactions, FeㅡC and FeㅡTi, are found to be the determinant factors for the adhesion strength at the interface. Higher adhesion properties can be attained when the surface Fe atoms are positioned directly over the surface C atoms of the carbide. This article presents a systematic perspective of the bonding nature at the Fe/TiC interface from a viewpoint of both the FeㅡC and FeㅡTi interactions.

TiO2(110) 표면에 흡착된 물분자의 결합 활성화에 관한 MO연구

강대복 대한화학회 2002 대한화학회지 Vol.46 No.3

La₇Os₄C₉의 전자구조와 화학결합

강대복,Kang, Dae-Bok 대한화학회 2009 대한화학회지 Vol.53 No.3

고체 화합물 La7Os4C9 속에 있는 [Os4C9]21? 사슬의 전자구조와 화학결합을 extended Huckel 계산 결과에 의해서 논의하였다. 탄소 원자는 물론 (C2)2? 분자의 결합 특성은 비교적 큰 Os-C 상호작용을 나 타내었고 특히 (C2)2? 분자의 결합길이 증가는 Fermi level 바로 아래에 Os-C2(1 πg) 결합 밴드의 존재로 인 해서 반결합 1πg 오비탈에 부분적인 전자점유가 일어나기 때문인 것으로 해석된다. In the recently synthesized rare earth transition metal carbide $La_7O_{s4}C_9$ one finds one-dimensional organometallic $[O_{s4}C_9]^{21-}$ polymers embedded in a $La^{3+}$ ionic matrix. The electronic structure of the polymeric $[O_{s4}C_9]^{21-}$ chain was investigated by density of states (DOS) and crystal orbital overlap population (COOP), using the extended Huckel algorithm. A fragment molecular orbital analysis is used to study the bonding characteristics of the $C_2$ units in $La_7O_{s4}C_9$ containing $C_2$ units and single C atoms as well. The title compound contains partially filled Os and carbon bands leading to metallic conductivity. As the observed distances already indicated, the calculations show extensive Os-C interactions. The C-C bond distance in the diatomic $C_2$ units ($d_{C-C}$=131 pm) in the solid is significantly increased relative to $${C_2}^{2-}$$ or acetylene, because antibonding $1{\pi}_g$ orbitals are partially filled by the Os-$C_2(1\;{\pi}_g)$ bonding contribution found at and below the Fermi level.

Structural Arrangements and Bonding Analysis of MgB2C2

강대복 대한화학회 2010 Bulletin of the Korean Chemical Society Vol.31 No.9

The orthorhombic MgB2C2 structure contains well-separated parallel graphite-like B2C22‒ layers which extend infinitely in two dimensions. Three possible ways to distribute B and C atoms in the hexagonal sublattice sites are adopted. Band structures for the hypothetical distribution patterns are examined to assess the electronic stability of these phases and to account for the observed arrangement by means of extended Hückel tight-binding calculations. The preferred choice is the layer with B and C alternating strictly so that B is nearest neighbor to C and vice versa. A rationale for this is given. Due to the alternation of B and C within the honeycomb layers, MgB2C2 is a band insulator, which through partial substitution of Mg with Li, is predicted to turn metallic with holes in the σ bands at the Fermi level.

Influence of Carbon Vacancies on CO Chemisorption on TiC(001): A Theoretical Study

강대복 대한화학회 2017 대한화학회지 Vol.61 No.1

The extended Hückel method is employed to analyze the interaction of carbon monoxide with the TiC(001) surfaces, both perfect and containing carbon vacancies. CO exhibits a similar σ-donation interaction for both Ti25C25 and Ti25C23 clusters, as deduced from the fact that the populations of the CO 5σ orbital are identical upon adsorption, but it bonds more strongly with the Ti25C23 than with the Ti25C25 because the metal d electron density in Ti25C23 provides π back-bonding interactions with CO that are absent in Ti25C25. This work suggests that a difference in reactivity toward CO of stoichiometric TiC and TiC with carbon defects is connected with the occupancy of 2π* orbitals that leads to a significant weakening of the C-O bond.

Effect of Valence Electron Concentration on Elastic Properties of 4d Transition Metal Carbides MC (M = Y, Zr, Nb, and Rh)

강대복 대한화학회 2013 Bulletin of the Korean Chemical Society Vol.34 No.7

The electronic structure and elastic properties of the 4d transition metal carbides MC (M = Y, Zr, Nb, Rh) were studied by means of extended Hückel tight-binding band electronic structure calculations. As the valence electron population of M increases, the bulk modulus of the MC compounds in the rocksalt structure does not increase monotonically. The dominant covalent bonding in these compounds is found to be M-C bonding, which mainly arises from the interaction between M 4d and C 2p orbitals. The bonding characteristics between M and C atoms affecting the variation of the bulk modulus can be understood on the basis of their electronic structure. The increasing bulk modulus from YC to NbC is associated with stronger interactions between M 4d and C 2p orbitals and the successive filling of M 4d-C 2p bonding states. The decreased bulk modulus for RhC is related to the partial occupation of Rh-C antibonding states.