제일원리 계산을 활용한 전기화학 촉매 연구

김동연 한국전기전자재료학회 2021 전기전자재료학회논문지 Vol.34 No.6

As the recent climate problems are getting worse year after year, the demands for clean energy materials have highly increased in modern society. However, the candidate material classes for clean energy expand rapidly and the outcomes are too complex to be interpreted at laboratory scale (e.g., multicomponent materials). In order to overcome these issues, the firstprinciples calculations are becoming attractive in the field of material science. The calculations can be performed rapidly using virtual environments without physical limitations in a vast candidate pool, and theory can address the origin of activity through the calculations of electronic structure of materials, even if the structure of material is too complex. Therefore, in terms of the latest trends, we report academic progress related to the first-principles calculations for design of efficient electrocatalysts. The basic background for theory and specific research examples are reported together with the perspective on the design of novel materials using first-principles calculations.

Predictions on Atomic Structures of Ti1-xMoxC using Combined Approach of First-Principles Calculation and the Cluster Expansion Method

이승철,이영수,정우상,최정혜 대한금속·재료학회 2009 METALS AND MATERIALS International Vol.15 No.5

Recently, binary transition metal carbides such as (Ti1-xMox)C have attracted much attention for use in increasing the strength of steels. This study aims to understand the ground state structure of various compositions of that carbide. Using a combined approach of first-principles calculation and the cluster expansion method, ground state structures of the compositions of TiC and MoC were determined. Only 29 symmetrically inequivalent structures were sufficient to determine the ground state structures of (Ti1-xMox)C for the whole range of the composition. The linear chains of solute atoms predicted by calculation were favored when the compositions of MoC were between 20 at.% and 70 at.%. When the composition of MoC was 50 at.%, an alternating layer of Ti and Mo formed along the <111> direction. This layered structure is expected to show peculiar mechanical and electronic properties. Recently, binary transition metal carbides such as (Ti1-xMox)C have attracted much attention for use in increasing the strength of steels. This study aims to understand the ground state structure of various compositions of that carbide. Using a combined approach of first-principles calculation and the cluster expansion method, ground state structures of the compositions of TiC and MoC were determined. Only 29 symmetrically inequivalent structures were sufficient to determine the ground state structures of (Ti1-xMox)C for the whole range of the composition. The linear chains of solute atoms predicted by calculation were favored when the compositions of MoC were between 20 at.% and 70 at.%. When the composition of MoC was 50 at.%, an alternating layer of Ti and Mo formed along the <111> direction. This layered structure is expected to show peculiar mechanical and electronic properties.

Ordered Phases in Fe-Si Alloys: A First-Principles Study

최영원,구양모,권세균,Levente Vitos 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.72 No.6

It is known that the formation of ordered phases causes the brittleness of electrical steels. We employed first-principles method in order to examine the possibility of the ordered-phases formation in Fe-Si alloys. It is found that the D03-like ordered configuration is most stable among other atomic configurations in the ferromagnetic state. In the paramagnetic state, for low Si concentration, the stability of the ordered configurations is comparable to that of disordered ones. However, as Si content increases, the B2 ordered phase as well as the D03 phase becomes more stable than the disordered ones.

The Half-Metallicity of Co2FeGe Full Heusler Alloy in (001) Thin Film: First Principles Study

현정민,김미영 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.72 No.2

The electronic and magnetic properties of the Co2FeGe full Heusler alloy in (001) thin film are investigated using the first-principles electronic structure calculations within the density functional theory. We employ various exchange correlation functionals including the local density approximation (LDA), the generalized gradient approximation (GGA), and the additional +U corrections for strong on-site Coulomb interaction of transition metal 3d states, aiming to examine the correlation effect on the electronic structures which determine the spin gap and thus the half-metallicity. Our results reveal that the Co2FeGe thin film is metallic in both LDA and GGA, while the +U correction opens up the spin gap for spin minority channel in GGA+U but not in LDA+U in contrast to its bulk alloy which is predicted to be half-metallic in both LDA+U and GGA+U approaches with total spin magnetic moment of 6 μB. It is found that the surface states developed around the Fermi level and the enhanced 3d eg-t2g band splitting for the spin minority channel due to the correlation effect play critical roles to determine the emergence of the half-metallicity.

First-principles study of lithium-ion diffusion in β-Li3PS4 for solid-state electrolytes

임명수,지승훈 한국물리학회 2018 Current Applied Physics Vol.18 No.5

Understanding the role of partially occupied sites in Li-based superionic conductors is key to improving performance of solid-state electrolyte materials. We study the optimized structure of crystalline β-Li3PS4 and the Liion diffusion using first-principles calculations and the nudged elastic band method. Considering diffusion paths through both interstitial and vacancy exchanges, we calculate the migration energies of Li ions. We find that the phonon-mode softening and concurrent inversion symmetry breaking leads to a more stable structure with low symmetry. Atomic distortion from the phonon softening provides diffusion paths for Li ions with less migration energies than the ones in high-symmetry structures. Our results show that diffusion of Li ion is highly anisotropic through the armchair- or zigzag-shaped channels along the b-axis that contain Li-ion sites with fractional occupation.

알루미늄 도핑된 스피넬 구조에서의 얀-텔러 효과의 이해

김두호(Duho Kim),임진명(Jin-Myoung Lim),황태순(Taesoon Hwang),조경재(Kyeongjae Cho),조맹효(Maenghyo Cho) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11

Through first-principles calculations and experimental observations, we present the fundamental understanding of mechanism of the suppression of Jahn-Teller effects using Al doping in the cubic spinel oxide (LiMn2O4). The Al-doped spinel exhibits better cycle stability as compared with the pristine spinel. Considering partial density of states (PDOS) and band fillings of the two oxides from the first-principles calculations, the pristine spinel is entirely suffered from Jahn-Teller distortion by Mn3+, indicating the anisotropic electronic structure. On the other hand, the Al-doped spinel shows suppressed Jahn-Teller effects, presenting the isotropic electronic structure. These findings based on the mechanistic understanding of Jahn-Teller effects are expected to be a basic solution and design new cathodes for the electrochemically enhanced properties in Li-ion batteries.

Sn 다형체의 온도에 따른 구조 상전이 현상에 대한 제일원리 연구

장성민,박철홍 한국물리학회 2019 새물리 Vol.69 No.3

Based on first-principles electronic structure calculations, we estimated the variations in the thermodynamic free energies of lattice vibrations with temperature for various polymorph structures of Sn: we examined the and polymorphs, two kinds of hexagonal structures, through which we are able to investigate their thermal-induced phase- transition characteristics. Similar to the experimental results, a phase transition from alpha-Sn to beta-Sn was observed with increasing temperature, because the entropy of beta-Sn is larger than that of alpha-Sn. Thus, the entropy effect of phonons appears to have played an important role in the phase transition. The hexagonal structure can be more stable than the beta structure at a high temperature, but the transition temperature was higher than the melting temperature of Sn; thus, hexagonal Sn is thought to be a metastable phase. 제일원리 전자구조 계산을 통하여, Sn의 다형체 구조 alpha 와 beta 구조, 그리고 hexagonal구조의온도에 따른 안정성과 상전이 현상의 열역학적 특성 연구하였다. 전자에너지와 포논의 열에너지와 엔트로피를 포함하는 자유에너지를 합성하여, 온도에 따른 총에너지 변화를 비교하여, 온도에 따른 구조 상전이를계산하였다. 계산 결과는 alpha구조에서 beta구조로 상전이가 일어날 수 있는 것을 보여 주었다. 하지만, 최근 박막성장 기술로 제작된 hexagonal(H)구조의 자유에너지를 이미 알려진 alpha구조 및 beta구조의총에너지와 비교한 결과, Sn의 융해 온도 보다 높은 온도에서 beta구조에서 H구조로 상전이가 일어날 수있음을 보였다. 즉, 본 계산 결과는 H가 준안정상태임을 보여 준다.

First-Principles Study on the Adsorption Properties of Transition-Metal Atoms on CaO(001) Surfaces

유병덕,장영록 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.70 No.6

By using first-principles electronic-structure calculations based on the density functional theory, we systematically investigated the adsorption properties of transition-metal (TM) adatoms on CaO(001) surfaces. Optimized adsorption structures and energetics of TM adatoms on CaO(001) are reported for various adsorption structures. The results are different from those of TM adatoms on MgO(001). Concomitantly, this suggests different dynamical properties of TM adatoms on CaO(001) surfaces as compared with TM adatoms on MgO(001) surfaces. Also performed was an analysis of the electronic structures of the TM adatoms on CaO(001) by using the energy positions of the adsorbate states with respect to the valence band maximum of CaO. The results are discussed in connection with the charge states of the TM adatoms on doped CaO(001).

전기화학적 암모니아 합성을 위한 루테늄 촉매 표면에서의 질소 환원반응 메커니즘 해석의 위한 제1원리 모델링

이상헌,조미현 한국화학공학회 2023 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.61 No.4

Electrochemical ammonia production using catalysts offers a promising alternative to the conventional Haber-Bosch process, allowing for ambient temperature and pressure conditions, environmentally friendly operations, and high-purity ammonia production. In this study, we focus on the nitrogen reduction reactions occurring on the surfaces of ruthenium catalysts, employing first-principles calculations. By modeling reaction pathways for nitrogen reduction on the (0001) and (1000) surfaces of ruthenium, we optimized the reaction structures and predicted favorable pathways for each step. We found that the adsorption configuration of N2 on each surface significantly influenced subsequent reaction activities. On the (0001) surface of ruthenium, the end-on configuration, where nitrogen molecules adsorb perpendicularly to the surface, exhibited the most favorable N2 adsorption energy. Similarly, on the (1000) surface, the end-on configuration showed the most stable adsorption energy values. Subsequently, through optimized hydrogen adsorption in both distal and alternating configurations, we theoretically elucidated the complete reaction pathways required for the final desorption of NH3.

First-principles study of the field-induced current-switch by dithiocarboxylate anchoring group in molecular junction

Caijuan Xia,Changfeng Fang,Peng Zhao,Desheng Liu 한국물리학회 2010 Current Applied Physics Vol.10 No.3

Based on non-equilibrium Green’s function and first-principles calculations, we investigate the electronic transport properties of 4,40-biphenyl bis (dithiocarboxylate) (BDCT) molecular junction with the fieldinduced geometry relaxation. The results indicate that the external field has noticeable effects on the molecular structure, coupling strengths and bonding distances. More importantly, it is found that the inclusion of field-induced molecular geometry relaxation can predict a current-switch behavior, which may have some potential applications in future molecular circuit.