• Title/Summary/Keyword: First principle calculations

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Calculation on Effect of Impurity Addition on Electronic State of $MnO_2$ Oxide Semiconductor by First Principle Moleculat Orbital Method (제1원리 분자궤도계산법에 의한 $MnO_2$ 산화물 반도체의 전자상태에 미치는 불순물 첨가 효과의 계산)

  • Lee, Dong-Yoon;Kim, Bong-Seo;Song, Jae-Sung;Kim, Hyun-Sik
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2003.11a
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    • pp.99-102
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    • 2003
  • The electronic structure of ${\beta}-MnO_2$ having impurities in the site of Mn was theoretically investigated by $DV-X_{\alpha}$ (the discrete variation $X{\alpha}$) method, which is a sort of the first principle molecular orbital method using Hatre-Fock-Slater approximation. The used cluster model was $[Mn_{14}MO_{56}]^{-52}$ (M = transient metals). Madelung potential and spin polarization were considered for more exact calculations. As results of calculations, the energy levels of all electron included in the model were obtained. The energy band gap and positions of impurity levies were discussed in association with impurity 34 orbital that seriously affect electrical properties of $MnO_2$. It was shown that the energy band gap decreased with the increase of the atomic number of transient metal impurity.

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First-principles Predictions of Structures and Piezoelectric Properties of PbTiO3 Single Crystal

  • Kim, Min Chan;Lee, Sang Goo;Joh, Cheeyoung;Seo, Hee Seon
    • Transactions on Electrical and Electronic Materials
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    • v.17 no.1
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    • pp.29-32
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    • 2016
  • Using the various exchange-correlation functionals, such as LDA, GGA-PBE, GGA-PBEsol and GGA-AM05 functionals, first principle studies were conducted to determine the structures of paraelectric and ferroelectric PbTiO3. Based on the structures determined by the various functionals, the piezoelectric properties of PbTiO3 are predicted under the density-functional perturbation theory (DFPT). The present prediction with the various GGA functionals are closer to the experimental findings compared to the LDA values. The present DFT calculations using the GGA-PBEsol functional estimate the experimental data more reasonably than the conventional LDA and GGA fucntionals. The GGA-AM05 functional also predicts the experimental data as well as the GGA-PBEsol. The piezoelectric tensor calculated with PBEsol is relatively insensitive to pressure.

Computational study of protactinium incorporation effects in Th and Th compounds

  • Daroca, D. Perez;Llois, A.M.;Mosca, H.O.
    • Nuclear Engineering and Technology
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    • v.52 no.10
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    • pp.2285-2289
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    • 2020
  • Protactinium contamination is a mayor issue in the thorium fuel cycle. We investigate, in this work, the consequences of Pa incorporation in vacancy defects and interstitials in Th, ThC and ThN. We calculate charge transfers and lattice distortions due to these incorporations as well as migration paths and energies involved in the diffusion of Pa.

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

  • Gang, Jun-Hui;Hwang, Ji-Min;Han, Byeong-Chan
    • Proceedings of the Korean Institute of Surface Engineering Conference
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    • 2017.05a
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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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Luminescence Behavior of $YNbO_4$ and $YNbO_4:Bi$

  • Chang, Hyun-Ju;Lee, Seung-Kwon;Han, Cheong-Hwa;Park, Hee-Dong
    • 한국정보디스플레이학회:학술대회논문집
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    • 2000.01a
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    • pp.35-36
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    • 2000
  • The luminescence behaviors of Yttrium niobate and Bi doped Yttrium niobate were investigated under UV and low voltage electron excitations and interpreted with the first-principle calculations. In the UV excitation and emission spectra of $YNbO_4$ and $YNbO_4:Bi$, we were able to separate host contribution and Bi contribution and found that the shift in emission peak to longer wavelength is mainly due to Bi contribution. Using density functional theory, the cluster calculations were carried out for both $YNbO_4$ and $YNbO_4:Bi$. From the calculated density of states, we were also able to explain the charge transfer gap in the host and the effect of Bi in the excitation and emission spectra theoretically.

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Structural characteristics and electronic properties of GaN with $N_V,\;O_N,\;and\;N_V-O_N$: first-principles calculations

  • Lee, Sung-Ho;Chung, Yong-Chae
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.17 no.5
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    • pp.192-195
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    • 2007
  • Structural and electronic properties of bulk GaN with nitrogen vacancy($V_N$), oxygen substitution on nitrogen site($O_N$), and complex of nitrogen vacancy and oxygen substitution on nitrogen site($V_N-O_N$) were investigated using the first principle calculations. It was found that stability of defect formation is dependent on the epilayer growth conditions. The complex of $V_N-O_N$ is energetically the most favorable state in a condition of Ga-rich, however, oxygen substitution in nitrogen site is the most favorable state in N-rich condition. The electronic property of complex with negative charge states at $\Gamma$ point was changed from semiconductor to metal. On the contrary, the properties of nitrogen vacancy except for neutral charge state have shown the semiconductor characteristics at $\Gamma$ point. In the oxygen substitution on nitrogen site, the energy differences between conduction band minimum and Fermi level were smaller than that of defect-free GaN.