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성동철,박노정,홍석륜 한국물리학회 2011 새물리 Vol.61 No.3
We have performed density functional theory (DFT) calculations to find the low-energy structure of various types of small metal clusters. We investigated the electronic structure of M13 clusters consisting of Al, Au, and transition metal atoms, such as Pd, Pt and Ti. Icosahedron and cuboctahedron consisting of 13 atoms are minimal cluster shapes of closed atomic shells. As a result,we found low-energy structures for several metal clusters. For the cases of Al and Ti clusters, the icosahedron structure has the lowest energy. On the other hand, gold clusters are flake-like, and Pd and Pt clusters have a cage shape for their low-energy structures. Finally, we calculated the magnetic moments of the transition metal clusters. 이 논문에서는 다양한 종류의 금속 클러스터에 대한 안정된 구조를 찾기위하여 제일원리 밀도범함수 이론을 이용한 연구를 수행하였다. 먼저우리는 13개의 원자로 이루어진 알루미늄과 금, 그리고 팔라듐, 백금,타이타늄과 같은 전이금속에 대한 전자구조를 조사하였다. 정십이면체(icosahedron)와 육팔면체(cuboctahedron)은 가장 작은 수의닫힌 원자껍질을 가지는 구조이다. 우리는 이 구조를 기본으로 금속원자13개로 이루어진 클러스터의 안정된 구조를 얻기 위해서 클러스터의모양을 여러 형태로 바꿔서 계산을 하였다. 그 결과, 알루미늄과타이타늄은 정십이면체 구조가 가장 안정된 구조이고, 팔라듐과 백금은새장(cage) 구조, 금은 박편(flake) 구조가 가장 안정된 구조임을 알게되었다. 마지막으로 각 금속클러스터의 구조에 따른 자기모멘트(magnetic moment)를 계산하였다.
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Van der Waals Density Functional Theory Study of Molecular Adsorbates on MoX2(X = S, Se or Te)
차장환,성동철,민경아,홍석륜 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.73 No.1
We have investigated binding properties between molecular adsorbates and transition metal dichalcogenide (TMD) such as MoS2, MoSe2, and MoTe2 using density functional theory (DFT) calculations with various van der Waals (vdW) functionals. It is found that calculated lattice parameters of MoX2 (X = S, Se, or Te) obtained by the vdW functionals give the relative errors of up to ±5% with respect to the experimental values. Depending on the binding behaviors of molecular adsorbates on MoX2 surface, the vdW functionals can be classified into three group; (1) DFT-D2, DFT-D3, DFT-D3(BJ), DFT-TS, and optB86b-vdW, (2) DFT-TS-SCS, and (3) optB88- vdW, optPBE-vdW, revPBE-vdW, and rPW86-vdW2 functionals. Moreover, we find that the optPBE-vdW functionals show relatively large binding energies, while DFT-TS-SCS functionals show relatively small binding energies between molecular adsorbates and MoX2.
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Spatial variation in the electronic structures of carpetlike graphene nanoribbons and sheets
민경아,성동철,류정아,김건,홍석륜 한국물리학회 2014 Current Applied Physics Vol.14 No.12
Graphene, when deposited on a supporting substrate with a step edge, may be deformed in the presence of the step edges of the substrate. In this study, we have investigated a spatial variation in the local electronic structure near the step region, by performing first-principles calculations for carpetlike armchair graphene nanoribbons (C-AGNR) and two-dimensional periodic carpetlike graphene sheets (PCGS). Our results indicate no practical difference in the local density of states (LDOS) between those of flat and step regions. Interestingly, however, the PCGS shows a remarkable variation in the LDOS with an external electric field (E-field). Furthermore, we also discuss the dependence of the direction and the magnitude of the applied E-field on the spatial variation in the LDOS.
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차장환,민경아,성동철,홍석륜 한국물리학회 2018 Current Applied Physics Vol.18 No.9
Two dimensional (2D) semiconducting materials such as MoS2 have been actively investigated for their applications in nanodevices and gas sensors (or detectors). In this connection, we have investigated atomic and electronic structures of specific adsorbates on the surface of MoS2 and the edge of MoS2 armchair nanoribbons (ANRs) using density functional theory (DFT) calculations. Our calculations reveal that molecular adsorbates are well adsorbed at the edge of MoS2 than on the surface of MoS2. Despite the weak van der Waals (vdW) interaction between molecular adsorbates and MoS2 surface, paramagnetic molecules such as NO and NO2 induce the reduced band gap in MoS2 by making the states within the bandgap. On the other hand, adsorbed CO, NO, NO2, and O2 at the edge of MoS2 ANRs have much influence on the band structures of MoS2 ANRs via dissociation into their constituent atoms, while adsorbed CO2, NH3, H2, and N2 at the edge of MoS2 ANRs do not much change the band structure of MoS2 ANRs due to no dissociation. Further, we identify that dissociated molecules rearrange the charge densities of MoS2 ANRs by making the states within the bandgap.
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