• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.367-367
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• 2010

The adsorption configurations of S-proline on Ge(100) were studied using scanning tunneling microscopy (STM), density functional theory (DFT) calculations, and high-resolution core-level photoemission spectroscopy (HRCLPES). We identified three adsorption structures of S-proline on Ge(100) through analysis of the STM images, DFT calculations, and HRCLPES results: (i) an 'intrarow O - H dissociated and N dative bonded structure', (ii) an 'O - H dissociation structure', and (iii) an 'N dative bonded structure'. Moreover, because adsorption through the N atom of S-proline produces a new chiral center due to symmetry reduction by N dative bonding, the adsorption configurations have either (R,S) or (S,S) chirality, yielding an (R,S)-'intrarow O - H dissociated and N dative bonded structure' and an (R,S)-'N dative bonded structure', with a preference for reaction at the Re face. This work presents a novel method for generating stereoselective attachment using S-proline molecules adsorbed onto a Ge(100) surface.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 하계학술대회 논문집 Vol.6
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• pp.172-173
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• 2005

The electronic state of ZnO doped with Y was calculated using the density functional theory. In this study, the program used for the calculation on theoretical structures of ZnO and doped ZnO was Vienna Ab-initio Simulation Package (VASP), which is a sort of pseudo potential method. The detail of electronic structure was obtained by the descrite variational $X\alpha$ (DV-$X\alpha$) method, which is a sort of molecular orbital full potential method. The optimized crystal structures obtained by calculations were compared to the measured structure. The density of state and energy levels of dopant elements was shown and discussed in association with optical properties.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2011년도 임시총회 및 하계학술연구발표회
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• pp.129-129
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• 2011

The limited understanding of the surface properties of $Pt_3Ni$ for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cell (PEMFC) has motivated the study of properties and electronic structures of seven layered $Pt_3Ni$ (001), (110), and (111) surfaces. The first principle method based on density functional theory (DFT) is carried out. It is found that the bulk $Pt_3Ni$ has a ferromagnetic ground state with the ordered fcc type L12 structure, which is in good agreement with other results. Non magnetic Pt has the induced magnetic moment due to the strong hybridization between 3d Ni and 5d Pt. The magnetic moment of Pt and Ni enhanced on the surface of each due to surface effect however the magnetic moment of surface Pt in the Pt-segregated Pt3Ni (111) decreased and the magnetic moment of Ni in Ni rich subsurface increased significantly. The calculated d band centers of Pt explain the possibilities for oxygen absorption and play the important roles in altering the catalytic properties. The spin polarized densities of states are presented in order to understand physical properties of Pt in different surfaces in detail.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2011년도 자성 및 자성재료 국제학술대회
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• pp.14-14
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• 2011

Limited understanding of the surface properties of $Pt_3Ni$ for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cell (PEMFC) has motivated the study of magnetic properties and electronic structures of Pt segregated $Pt_3Ni$ (111) surface during adsorption of oxygen molecule on it. The first principle method based on density functional theory (DFT) is carried out. Nonmagnetic Pt has induced magnetic moment due to strong hybridization between Ni 3d and Pt 5d. It is found that an oxygen molecule prefers bridge site with Pt rich subsurface environment for adsorption on the surface of Pt segregated $Pt_3Ni$ (111). It is seen that there is very small charge transfer from $O_2$ to Pt. The curve of energy versus magnetic moment of the oxygen explains the magnetic moments in transition states. We found the dissociation barrier of 1.07eV significantly higher than dissociation barrier 0.77eV on Pt (111) suggesting that the dissociation is more difficult on Pt segregated $Pt_3Ni$ (111) surface. The spin polarized densities of states are presented in order to understand electronic structures of Pt and $O_2$ during the adsorption in detail.

• Bulletin of the Korean Chemical Society
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• 제30권9호
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• pp.2077-2082
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• 2009

The conformational and electronic properties of 2-cyano-3-(thiophen-2-yl)acrylic acid (TCA) in analogues used as sensitizers in dye-sensitized solar cells was examined using density functional theory (DFT) and natural bond orbital analysis methods. A relaxed potential energy surface scan was performed on NKX-2677 by rotating the C-C bond between the thiophene and cyanoacrylic acid which yielded activation energy barriers of about 13 kcal/mol for both E and Z configurations. The most stable conformation of all the analogues was E-180 except for NKX-2587 which has an electrostatic repulsion between the oxygen of the coumarin and the nitrogen of the cyanoacrylic acid. The increase in the electron delocalization between the thiophene and cyanoacrylic acid influences the stability for most of the analogues. But for NKX-2600, even though there was a greater deviation from the planarity of TCA, the stability was mainly due to the presence of a weak hydrogen bond between the hydrogen of the methyl group of the amine located in the donor moiety and the nitrogen of the cyanoacrylic acid. The vertical excitation energies of the analogues containing TCA were calculated by time-dependent DFT method. There were slight differences in its vertical excitation energies but the oscillator strengths vary significantly especially in the case of NKX-2600.

• Bulletin of the Korean Chemical Society
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• 제31권4호
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• pp.881-886
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• 2010

A novel Schiff base N-(2,4-dinitro-phenyl)-N'-(1-phenyl-ethylidene)-hydrazine has been synthesized and structurally characterized by X-ray single crystal diffraction, elemental analysis, IR spectra and UV-vis spectrum. The crystal belongs to monoclinic with space group P21/n. The molecules are connected via intermolecular O-$H{\cdots}O$ hydrogen bonds into 1D infinite chains. The crystal structure is consolidated by the intramolecular N-$H{\cdots}O$ hydrogen bonds. weak intermolecular C-$H{\cdots}O$ hydrogen bonds link the molecules into intriguing 3D framework. Furthermore, Density functional theory (DFT) calculations of the structure, stabilities, orbital energies, composition characteristics of some frontier molecular orbitals and Mulliken charge distributions of the title compound were performed by means of Gaussian 03W package and taking B3LYP/6-31G(d) basis set. The time-dependent DFT calculations have been employed to calculate the electronic spectrum of the title compound, and the UV-vis spectra has been discussed on this basis. The results show that DFT method at B3LYP/6-31G(d) level can well reproduce the structure of the title compound.

• Bulletin of the Korean Chemical Society
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• 제27권12호
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• pp.2051-2054
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• 2006

The molecular structures of the ground and lowest triplet states of 2,3-diazabicyclo[2.2.1]hept-2-ene (DBH), 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) and their fused ring derivatives are investigated with an ab initio method and the density functional theory. Unlike the singlet DBH and DBO, the azo skeletal structures of the triplet counterparts are turned out to be quite sensitive to the change of the electronic structure of the fused ring. The B3LYP C-N=N-C dihedral angles of the triplet DBH and DBO are estimated to be about 28.0 and $40.4{^{\circ}}$, respectively. The B3LYP singlet-triplet energy gaps for DBH and DBO are predicted to be 58.4 and 48.4 kcal/mol, respectively. The triplet state energy can be lowered drastically by the presence of the remote $\Pi-\Pi$ interaction as in the case of 1bb'.

• Bulletin of the Korean Chemical Society
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• 제34권2호
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• pp.453-459
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• 2013

In phtosynthetic light harvesting complexes, the electronic transition energies of chlorophylls are influenced by the Coulombic interaction with nearby molecules. Variation of the interactions caused by structural inhomogeneity in biological environment results in a distribution of disordered electronic transition energies of chlorophylls. In order to provide a practical guide to predict qualitative tendency of such distribution, we model four porphyrin derivatives including chlorophyll a molecule interacting with an external positive charge and calculate their transition energies using the time dependent density functional method. It is found that ${\pi}-{\pi}^*$ transition energies of the molecules are generally blue-shifted by the charge because this stabilizes occupied molecular orbitals to a greater extent than unoccupied ones. Furthermore, new transitions in the visible region emerge as a result of the red-shift in energy of an unoccupied Mg orbital and it is suggested that light-induced electron transfer may occur from the tetrapyrrole ring to the central magnesium when the molecules are interacting with a positive charge.

• Nuclear Engineering and Technology
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• 제54권8호
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• pp.2783-2791
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• 2022

Molecular dynamics simulations were performed to predict the behavior of graphite atoms under neutron irradiation using large-scale atomic/molecular massively parallel simulator (LAMMPS) package with adaptive intermolecular reactive empirical bond order (AIREBOM) potential. Defect structures of graphite were compared with results from previous studies by means of density functional theory (DFT) calculations. The quantitative relation between primary knock-on atom (PKA) energy and irradiation damage on graphite was calculated. and the effect of PKA direction on the amount of defects is estimated by counting displaced atoms. Defects are classified into four groups: structural defects, energy defects, vacancies, and near-defect structures, where a structural defect is further subdivided into six types by decision tree method which is one of the supervised machine learning techniques.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.438-438
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• 2011

White light-emitting diodes (LEDs), the so-called next-generation solid-state lighting, offer benefits in terms of reliability, energy-saving, maintenance, safety, lead-free, and eco-friendly. Recently, rare-earth-doped oxynitride or nitride compounds have attracted a great deal of interest as a photoluminescent material because of their unique luminescent property, especially for white LEDs applications. Ce doped ${\beta}$-SiAlON has been studied as a wavelength conversion phosphor in white LEDs thanks to its high absorption rates, high quantum efficiency, and excellent thermal stability. Previously researches were not enough to understand the detail mechanism and characteristics of ${\beta}$-SiALON. The bandgap structures and electronic structures were not exact due to limitation of calculation methods. In this study, to elucidate the Ce doping effect on the SiAlON system, accurate band structures and electronic structure of the Ce doped ${\beta}$-SiAlON was intensively investigated using density functional theory calculations. In order to get a better description of the band gaps, MBJLDA method were used. We have found a single Ce atom site in ${\beta}$-SiAlON super cell. Furthermore, the density of state, band structure and lattice constant were intensively investigated.