• 제목/요약/키워드: Density-functional theory

검색결과 501건 처리시간 0.032초

밀도함수 이론법을 이용한 마그네슘 합금의 재료특성 예측에 관한 연구 (A Study on the Prediction of the Material Properties of Magnesium Alloys Using Density Functional Theory Method)

  • 백민숙;원대희;김병일
    • 한국재료학회지
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    • 제17권12호
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    • pp.637-641
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    • 2007
  • The total energy and strength of Mg alloy doped with Al, Ca and Zn, were calculated using the density functional theory. The calculations was performed by two programs; the discrete variational $X{\alpha}\;(DV-X{\alpha})$ method, which is a sort of molecular orbital full potential method; Vienna Ab-initio Simulation Package (VASP), which is a sort of pseudo potential method. The fundamental mixed orbital structure in each energy level near the Fermi level was investigated with simple model using $DV-X{\alpha}$. The optimized crystal structures calculated by VASP were compared to the measured structure. The density of state and the energy levels of dopant elements was discussed in association with properties. When the lattice parameter obtained from this study was compared, it was slightly different from the theoretical value but it was similar to Mk, and we obtained the reliability of data. A parameter Mk obtained by the $DV-X{\alpha}$ method was proportional to electronegativity and inversely proportional to ionic radii. We can predict the mechanical properties because $\Delta{\overline{Mk}}$is proportional to hardness.

범밀도함수법을 이용하여 계산한 IIIB족 원소가 도핑된 ZnO의 전자상태 (Electronic State of ZnO Doped with Elements of IIIB family, Calculated by Density functional Theory)

  • 이동윤;이원재;민복기;김인성;송재성;김양수
    • 한국전기전자재료학회논문지
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    • 제18권7호
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    • pp.589-593
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    • 2005
  • The electronic states of ZnO doped with Al, Ga and In, which belong to III family elements in periodic table, were calculated using the density functional theory. In this study, the calculation was performed by two Programs; the discrete variational Xa (DV-Xa) method, which is a sort of molecular orbital full potential method; Vienna Ab-initio Simulation Package (VASP), which is a sort of pseudo potential method. The fundamental mixed orbital structure in each energy level near the Fermi level was investigated with simple model using DV-Xa. The optimized crystal structures calculated by VASP were compared to the measured structures. The density of state and the energy levels of dopant elements were shown and discussed in association with properties.

Density Functional Analysis of the Spin Exchange Interactions in VOSb2O4

  • Koo, Hyun-Joo
    • Bulletin of the Korean Chemical Society
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    • 제33권7호
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    • pp.2338-2340
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    • 2012
  • The spin exchange parameters of $VOSb_2O_4$ were evaluated by performing energy-mapping analysis based on density functional calculations. The spin exchange interaction between the nearest-neighbor $V^{4+}$ ions is strongly antiferromagnetic while other interactions are negligible. Thus, the magnetic structure of $VOSb_2O_4$ is best described by a spin-1/2 Heisenberg antiferromagnetic chain with no spin frustration.

{Ca,Sr,Ba}$Fe_2As_2$의 전자 및 자성 구조: 동력학적 평균장 이론 접근 (Electronic and Magnetic Structures of {Ca,Sr,Ba}$Fe_2As_2$ : Dynamical Mean Field Theory Approach)

  • 이근식;심지훈
    • Progress in Superconductivity
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    • 제13권2호
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    • pp.85-89
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    • 2011
  • 제일원리 DFT+DMFT방법을 사용하여 철계열 고온초전도체 122 화합물 $AFe_2As_2$ (A=Ca, Sr, Ba) 에 대한 전자 및 자성 구조를 계산하였다. 계산된 전자구조는 실험에서 보고된 ARPES 결과와 어느 정도 일치함을 확인했다. 또한 계산을 통해 얻은 반자성 전이온도는 실험과 동일한 경향을 보여준다.

수소발생반응에 대한 Pyrites 표면 촉매 성능 예측: 밀도 범함수 이론 계산 (Identification of a Universal Relation between a Thermodynamic Variable and Catalytic Activities of Pyrites toward Hydrogen Evolution Reaction: Density Functional Theory Calculations)

  • 강준희;황지민;한병찬
    • 한국표면공학회:학술대회논문집
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    • 한국표면공학회 2017년도 춘계학술대회 논문집
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    • pp.87.1-87.1
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    • 2017
  • High functional catalyst to efficiently produce clean and earth-abundant renewable fuels plays a key role in securing energy sustainability and environmental protection of our society. Hydrogen has been considered as one of the most promising energy carrier as represented by focused research works on developing catalysts for the hydrogen evolution reaction (HER) from the water hydrolysis over the last several decades. So far, however, the major catalysts are expensive transition metals. Here using first principles density functional theory (DFT) calculations we screen various pyrites for HER by identifying fundamental descriptor governing the catalytic activity. We enable to capture a strong linearity between experimentally measured exchange current density in HER and calculated adsorption energy of hydrogen atom in the pyrites. The correlation implies that there is an underlying design principle tuning the catalytic activity of HER.

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분자의 전기음성도에 관한 이론적 고찰 (On the Electronegativity of Molecule)

  • 김호징;김종현
    • 대한화학회지
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    • 제29권1호
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    • pp.3-8
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    • 1985
  • Density functional theory에서의 전기음성도의 정의에 의해 전기음성도를 가전자(valence electron)만을 고려하여 구하였다. 전기음성도는 Hartree-Fock의 궤도 에너지(orbital energy)로 표시되는데 이로부터 구한 분자의 전기음성도 값은 다른 값들과 좋은 상관관계(correlation)를 보여준다. 또한 분자를 형성할 때 Sanderson의 법칙(electronegativity equalization principle)이 만족됨을 보였다.

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Theoretical Studies on Electronic Structure and Absorption Spectrum of Prototypical Technetium-Diphosphonate Complex 99mTc-MDP

  • Qiu, Ling;Lin, Jian-Guo;Gong, Xue-Dong;Ju, Xue-Hai;Luo, Shi-Neng
    • Bulletin of the Korean Chemical Society
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    • 제32권7호
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    • pp.2358-2368
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    • 2011
  • Density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations, employing the B3LYP method and the LANL2DZ, 6-31G$^*$(LANL2DZ for Tc), 6-31G$^*$(cc-pVDZ-pp for Tc) and DGDZVP basis sets, have been performed to investigate the electronic structures and absorption spectra of the technetium-99m-labeled methylenediphosphonate ($^{99m}Tc$-MDP) complex of the simplest diphosphonate ligand. The bonding situations and natural bond orbital compositions were studied by the Mulliken population analysis (MPA) and natural bond orbital (NBO) analysis. The results indicate that the ${\sigma}$ and ${\pi}$ contributions to the Tc-O bonds are strongly polarized towards the oxygen atoms and the ionic contribution to the Tc-O bonding is larger than the covalent contribution. The electronic transitions investigated by TDDFT calculations and molecular orbital analyses show that the origin of all absorption bands is ascribed to the ligand-to-metal charge transfer (LMCT) character. The solvent effect on the electronic structures and absorption spectra has also been studied by performing DFT and TDDFT calculations at the B3LYP/6-31G$^*$(cc-pVDZ-pp for Tc) level with the integral equation formalism polarized continuum model (IEFPCM) in different media. It is found that the absorption spectra display blue shift in different extents with the increase of solvent polarity.

범밀도함수이론에 기초한 니켈(100) 표면에서의 전기화학적 질소환원반응 메커니즘에 관한 연구 (A Density-Functional Theory Study on Mechanisms of the Electrochemical Nitrogen Reduction Reaction on the Nickel(100) Surface)

  • 김민지;이상헌
    • Korean Chemical Engineering Research
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    • 제61권4호
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    • pp.604-610
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    • 2023
  • 주변 조건에서 N2를 환원하여 NH3를 생성하는 전기 촉매 질소 환원 반응(nitrogen reduction reaction, NRR)은 산업공정에서 에너지 소비를 감소시킬 수 있는 유망한 기술로 주목을 받고 있다. N2를 흡착하고 활성화할 수 있는 촉매 금속 표면 중 많이 사용되는 Ni(100) 표면의 여러 사이트(site)의 흡착 성능을 밀도 함수 이론 계산(density-functional theory)를 기반으로 비교하였다. 또한 안정적인 NRR반응의 경로를 유도하는 N2의 두 가지 흡착 구조를 조사하였고 end-on 구조는 top site에 흡착, distal pathway로 반응이 진행되고 side-on 구조는 bridge site에 흡착되며 enzymatic pathway로 반응이 진행되었다. 마지막으로 구조 별 가장 안정한 메커니즘의 깁스 자유에너지를 구하여 반응의 경향성을 알아봄으로써 NRR 반응의 금속 촉매 표면 흡착에 대한 연구에 도움이 될 수 있을 것이다.

Electrostatic Adsorption of Uniformly Charged Electrolytes within Like-charged Electrodes

  • Jang, Seanea;Shin, Ghi Ryang;Kim, Soon-Chul
    • Journal of the Korean Physical Society
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    • 제73권9호
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    • pp.1315-1323
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    • 2018
  • The classical-fluids density functional theory has been developed for studying the structural and the electrical properties of electrolyte solutions containing uniformly charged hard-spherical ions. The modified fundamental-measure theory has been used to evaluate the hard-sphere contribution. The mean-field approximation has been employed to calculate the cross correlation between the hard sphere contribution and the Coulomb interaction. The Poisson equation for ions carrying charges that are spatially separated has been solved. The present theory shows reasonably good agreement with the corresponding Monte Carlo simulation results. The calculated results show that the attraction between like-charged planar surfaces is the result of the intra-ionic correlation and depends strongly on the ion size, valence, mole fraction, and charge distribution of electrolytes.

Time-Dependent Density Functional Theory Study on Cyclopentadithiophene-Benzothiadiazole-Based Push-Pull-Type Copolymers for New Design of Donor Materials in Bulk Heterojunction Organic Solar Cells

  • Ku, Ja-Min;Kim, Dae-Kyun;Ryu, Taek-Hee;Jung, Eun-Hwan;Lansac, Yves;Jang, Yun-Hee
    • Bulletin of the Korean Chemical Society
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    • 제33권3호
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    • pp.1029-1036
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    • 2012
  • Push-pull-type copolymers - low-band-gap copolymers of electron-rich fused-ring units (such as cyclopentadithiophene; CPDT) and electron-deficient units (such as benzothiadiazole; BT) - are promising donor materials for organic solar cells. Following a design principles proposed in our previous study, we investigate the electronic structure of a series of new CPDTBT derivatives with various electron-withdrawing groups using the time-dependent density functional theory and predict their power conversion efficiency from a newlydeveloped protocol using the Scharber diagram. Significantly improved efficiencies are expected for derivatives with carbonyl [C=O], carbonothioyl [C=S], dicyano [$C(CN)_2$] and dicyanomethylene [C=$C(CN)_2$] groups, but these polymers with no long alkyl side chain attached to them are likely to be insoluble in most organic solvents and inapplicable to low-cost solution processes. We thus devise several approaches to attach alkyl side chains to these polymers while keeping their high efficiencies.