• Journal of Korean Society of Environmental Engineers
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• v.38 no.5
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• pp.242-248
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• 2016

The overall reaction rate of fuel cell is governed by oxygen reduction reaction (ORR) in the cathode due to its slowest reaction compared to the oxidation of hydrogen in the anode. The ORR efficiency can be readily evaluated by examining the adsorption strength of atomic oxygen on the surface of catalysts (i.e., known as a descriptor) and the adsorption energy can be controlled by transforming the surface geometry of catalysts. In the current study, the effect of the surface geometry of catalysts (i.e., strain effect) on the adsorption strength of atomic oxygen on platinum catalysts was analyzed by using density functional theory (DFT). The optimized lattice constant of Pt ($3.977{\AA}$) was increased and decreased by 1% to apply tensile and compressive strain to the Pt surface. Then the oxygen adsorption strengths on the modified Pt surfaces were compared and the electron charge density of the O-adsorbed Pt surfaces was analyzed. As the interatomic distance increased, the oxygen adsorption strength became stronger and the d-band center of the Pt surface atoms was shifted toward the Fermi level, implying that anti-bonding orbitals were shifted to the conduction band from the valence band (i.e., the anti-bonding between O and Pt was less likely formed). Consequently, enhanced ORR efficiency may be expected if the surface Pt-Pt distance can be reduced by approximately 2~4% compared to the pure Pt owing to the moderately controlled oxygen binding strength for improved ORR.

• Journal of the Korean Chemical Society
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• v.61 no.1
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• pp.16-24
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• 2017

The adsorption of various atmospheric harmful gases ($CO_x$, $NO_x$, $SO_x$) on graphene-like boron nitride(BN) and aluminum nitride(AlN) sheets was theoretically investigated using density functional theory (DFT) and MP2 methods. The structures were fully optimized at the $B3LYP/6-31G^{**}$ and $CAM-B3LYP/6-31G^{**}$ levels of theory and confirmed to be a local minimum by the calculation of the harmonic vibrational frequencies. The MP2 single-point binding energies were computed at the $CAM-B3LYP/6-31G^{**}$ optimized geometries. Also the zero-point vibrational energy (ZPVE) and 50%-basis set superposition error (BSSE) corrections were included. The adsorptions of gases on the BN sheet were predicted to be a physisorption process and the adsorptions of gases on the AlN sheet were predicted to be a physisorption process for $CO_x$ and $NO_x$ but to be a chemisorption process for $SO_x$.

• Analytical Science and Technology
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• v.18 no.4
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• pp.309-319
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• 2005

The adsorption characteristics of gaseous molecules on the carbonaceous adsorbent have been investigated at various temperature and pressure with different pore sizes using Grand Canonical Monte Carlo (GCMC) simulation method. The geometrical parameters and spectroscopic properties of adsorbates have been computed using density functional theory (DFT). At higher temperatures is the adsorption amount of adsorbates is decreased due to their vaporization. Considering the pore size effect, the adsorption characteristic depends on the adsorbate size, polarity and interaction between adsorbates, etc. At all cases employed in this study, the adsorption amount of adsorbates on the carbonaceous adsorbent is increased in the order $NH_3$ < $H_2S$ < $CH_3SH$, and this result is qualitatively in good agreement with the experimental observation.

• Journal of the Korean Chemical Society
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• v.54 no.4
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• pp.363-373
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• 2010

Computational studies were carried out on the opiates morphine, heroin, codeine, pentazocine, and buprenorphine, under the density functional theory. The geometric parameters of the pharmacophore and substituents were evaluated at the B3LYP/6-31+G(d) level of theory. The electronic structure calculations were performed using the same hybrid functional at the B3LYP/6-311++G (d,p) level of theory. The atomic charges were obtained by Mulliken population analysis. Given the reported biological activity, calculated partition coefficients, and electronic and geometric analysis, pentazocine and buprenorphine were chosen as models for proposed analogues. These analogues were then studied and compared with the model molecules. The study reveals that the geometry and electronic structure of the pharmacophore remains consistent in the presence of different substituents. Because the proposed analogues preserve the studied properties of the model molecules, it is likely that these analogues display biological activity.

• Proceedings of the IEEK Conference
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• 2001.06d
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• pp.73-76
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• 2001

In this paper, we utilize a HVS(Human Visual System) watermarking method where watermarks are embedded in a DFT domain. The HVS watermarking method is robust for attacks like JPEC, filtering, noise, etc. But, when images are attacked by basic geometric attacks as cropping, scaling, rotation, a watermarks may not be detected. In this paper, we introduce the HVS watermarking method that inserts references In a domain of LSB(Least Significant Bit) of image. Experimental results show that the proposed method based on HVS watermarking method gives more robustness to the basic geometric attacks compared with original HVS watermarking methods.

• Proceeding of EDISON Challenge
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• 2014.03a
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• pp.511-513
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• 2014

$MoS_2$ monolayer에 Au 원자를 흡착시켰을 때 가장 안정한 위치를 찾아 내기위한 연구를 수행하였다. 이를 위하여 $MoS_2$ $1{\times}1$ unit cell 위의 on-top, bridge, hollow 위치에 Au 원자를 놓고 DFT 기반 제일원리 계산을 통하여 최적화된 구조에서의 에너지를 계산, 비교하였다. 그 결과 S 원자 위에 Au 원자가 흡착 되었을 때 가장 안정한 구조를 이루는 것을 알 수 있었다.

• Proceeding of EDISON Challenge
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• 2015.03a
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• pp.373-377
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• 2015

이 연구에서는 원자 궤도 함수 기반 DFT 전자구조 계산을 이용해서 최근 각광받고 있는 이차원 물질인 MoS2 monolayer의 S 자리와 Mo 자리에 각각 전자가가 다른 원자를 치환하였을 때의 도핑 특성을 Density of States (DOSs)와 밴드구조 등의 전자구조를 통해 분석해 보았다. S자리에 Cl, Si, I, B, C, Mo 자리에는 Hf, Ta, 그리고 Re을 치환해 보았으며 계산 결과 S자리에 Cl을 치환했을 때 가장 얕은 acceptor level (VBM으로부터 0.08 eV)이 형성되었으며, Mo자리에 Re를 치환했을 때에는 resonant state를 형성하였다. 또한 Mo자리에 Ta를 치환했을 ? 가장 얕은 donor level (CBM으로부터 0.02 eV)가 형성되었다.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.36S no.5
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• pp.96-103
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• 1999

본 논문에서는 sliding-DFT(SDFT)를 계수의 유한 비트 근사구현에 기초하여 실시간 구현하는 기법을 제시하고, 이의 오차영향을 해석하였다. 오차의 영향을 오차전력과 신호전력비율(noise-to-signal power ratio : NSR)로 하여 이를 해석적으로 유도하였다. 가우스 렌덤신호 및 사람의 수면 EEG 신호를 대상으로 수행한 시뮬레이션 결과가 해석식과 잘 일치하는 것을 보임으로써 본 연구에서 얻은 해석식을 확인하였다.

• Journal of the Mineralogical Society of Korea
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• v.31 no.1
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• pp.13-22
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• 2018

Aluminum silicates ($Al_2SiO_5$) undergo phase transitions among kyanite, andalusite, and sillimanite depending on temperature and pressure conditions. The minerals are often used as an important indicator of the degree of metamorphism for certain metamorphic rocks. In this study, we have applied classical molecular dynamics (MD) simulations and density functional theory (DFT) to the aluminum silicates. We examined the crystal structures as a function of applied pressure and the corresponding stabilities based on calculated enthalpies at each pressure. In terms of the lattice parameters, both methods showed that the volume decreases as the pressure increases as observed in the experiment. In particular, DFT results differed from experimental results by much less than 1%. As to the relative stability, however, both methods showed different levels of accuracy. In the MD simulations, a transition pressure at which the relative stability between two minerals reverse could not be determined because the enthalpies were insensitive to the applied pressure. On the other hand, in DFT calculations, the relative stability relation among the three minerals was consistent with experiment, although the transition pressure was strongly dependent on the choice of the electronic exchange-correlation functional.

• Journal of dental hygiene science
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• v.13 no.4
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• pp.426-433
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• 2013

The objective of this study was to examine whether there is an association of oral health conditions between mothers and their preschool children in Korea. A sample of 823 preschool children and their mothers were selected for this study from the database of the fourth Korean National Health and Nutrition examination Survey. Preschool children were defined as children aged 4, 5, and 6 years old. The subjects were clinically examined for the presence of caries lesions (dft index) and their mother was checked for the presence of dental caries (DMFT index) and periodontal status (CPI). The socio-demographic characteristics and mother's oral health behaviours were considered covariates in this study. Univariate and multivariate analysis was adapted to assess the association of oral health condition between mothers and their preschool children. In univariate analysis, there were significant differences between preschool children's dft index and their mother's age (p=0.005), dental treatment demand for the past one year (p=0.034), and DMFT index (p=0.016). In multivariate analysis, only mother's DMFT index was significantly associated with their children's dft index after adjusting for covariates. In conclusion, the mother's oral health was partly associated with their preschool children's oral health in Korea.