Effects of the Magnetic Part of The Breit Term on Bonding: Model Calculations with Small Diatomic Molecules

류설,한영규,이윤섭,Ryu, Seol,Kyoung K. Baeck,Han, Yeong Gyu,Lee, Yun Seop Korean Chemical Society 2001 Bulletin of the Korean Chemical Society Vol.22 No.9

Model calculations for small molecules Li2, F2, LiF and BF have been performed at the Dirac-Fock level of theory using Dirac-Coulomb and Dirac-Coulomb-Magnetic Hamiltonians with various basis sets. In order to understand what may happen when the relativity becomes significant, the value of c, speed of light, is varied from the true value of 137.036 a.u. to 105 (nonrelativistic case) and also to 50 and 20 a.u. (exaggerated relativistic cases). Qualitative trends are discussed with special emphasis on the effect of the magnetic part of the Breit interaction term. The known relativistic effects on bonding such as the bond length contraction or expansion are demonstrated in this model study. Total energy, $\pi-orbital$ splitting, bond length, bond dissociation energy and dipole moment are calculated, and shown to be modified in a uniform direction by the effect of the magnetic term. Inclusion of the magnetic term raises the total energy, increases the bond length, reduces the $\pi-orbital$ splitting, increases the bond dissociation energy, and mitigates the changes in dipole moment caused by the Dirac term.

선호매개변수를 이용한 삼중 임계격자장 비등방성의 계산

류설,곽우섭 한국물리학회 2013 새물리 Vol.63 No.9

We perform Monte Carlo simulations of the two-dimensional spin-1 Blume-Capel model by using the Wang-Landau sampling method, where the linear dimension L ranges 6, 8, 10, 12. We use the preference parameter to estimate the tricritial lattice field anisotropy from the crossing of the Binderïs fourth-order cumulants U4 for successive system sizes and compare it with that obtained by using the order parameter (magnetization) at a known tricritical temperature kBTt/J = 0.609. We obtain the tricritical lattice flied anisotropies at Dt/J = 1.964(9) by using the preference parameter and at Dt/J = 1.962(9) by using the order parameter. We find that compared to the order parameter, the preference parameter works well and improves the simulation performance. 이차원 입방격자에서 스핀-1 블룸-카펠 모형을 왕-란다우 표본잡기를사용하여 길이차원 L= 6, 8, 10, 12 에서 몬테칼로 전산시늉을 수행하였다. 알려진 삼중 임계온도 kBTt/J = 0.609 에서선호매개변수와 질서매개변수 (자화량) 의 빈더의사차 큐뮬런트 U4의길이차원에 따른 교점을 이용하여 삼중 임계격자장의 비등방성을계산하여 비교하였다 삼중 임계격자장의 비등방성은 선호매개변수는Dt/J=1.964(9)이고 질서매개변수는 Dt/J=1.962(9)로계산되었다. 우리는 선호매개변수가 삼중 임계격자장의 비등방성을정확히 계산할 수 있으며, 질서매개변수와 비교하여 전산시늉의 성능또한 개선한다는 결과를 연구를 통하여 얻게 되었다.

왕란다우 알고리듬을 이용한 두가지 다른 상태밀도의 분포 계산

류설,곽우섭 한국물리학회 2012 새물리 Vol.62 No.9

We perform a simulation of the Ising model by using the Wang-Landau algorithm, and we compare the simulation results obtained from the density of state g(E_1)with a histogram H(E_1,E_2) to those obtained from the joint density of state g(E_1,E_2). We found that the simulation results without an estimate of the joint density of states yield a biased distribution of the order parameter. 왕-란다우 표본 추출 방법 (Wang-Landau algorithm)을 사용하여전산시늉을 수행할 때, 연계상태밀도 (joint density of states)를 직접구하거나 혹은 상태밀도 (density of states)와 히스토그램(histogram)을 따로 구하는 방법이 주로 사용된다. 우리는 본 논문에서히스토그램과 상태밀도를 따로 구하는 방법으로 전산시늉을 수행하면질서맺음변수 (order parameter)가 편향된다는 결과를 아이징모형(Ising model) 연구를 통하여 얻게 되었다.

Structures of Butylthiolate Self-Assembled Monolayers on Au(111) with Gold Adatoms

류설,이윤섭,강지원,한영규 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.10

A density functional theory method with the local basis set was employed to perform slab calculations to study thiolate-induced surface reconstruction structures of butylthiolates (ButS) with c(4 × 2) superlattice of the Au(111) surface. The slab calculations indicate that the most stable adsorption structure is the ButS-Au (adatom)-SBut complex form, which is in good agreement with the reported experiments and theoretical results for thiolates with shorter alkyl chains. The cis form of ButS-Au (adatom)-SBut motifs is preferred by 0.11 eV with respect to the trans form, and by 0.15 eV over the mixed cis-trans configurations due to the steric hindrance between adjacent butyl groups. It appears that the motif of Au adatom on the Au(111) surface is favored even for butylthiolate.

A Density Functional Study of Amine Catalysts for CO2 Fixation into Cyclic Carbonates

류설 대한화학회 2019 Bulletin of the Korean Chemical Society Vol.40 No.10

The catalytic efficiency of three different kinds of amine groups for a prototype reaction of propylene oxide and carbon dioxide was investigated using density functional and energetic span model calculation. Our study demonstrated that tertiary amine groups perform best as catalyst at 100?°C and 10 bars because the corresponding catalytic cycle is free of any proton to be transferred around different molecular fragments. With primary or secondary amine catalysts, however, one or two protons at the nitrogen atom of amine can be transferred to the oxide oxygen, leading to intermediate structures stabilized by intramolecular hydrogen bonding at a deep valley in catalytic cycle. It is concluded that, when compared with the cases of primary or secondary amine groups, the effectiveness of tertiary amine group in catalysis originates from least hindrance to final products in catalytic cycle due to the absence of protons transferred.

Performance of Density Functionals for the Calculation of Gold Clusters

류설,Hyun Won Lee,한영규 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.8

신경 펩타이드 Met-enkephalin의 분배함수 근 이론 연구

류설,김승연,곽우섭 한국물리학회 2014 새물리 Vol.64 No.8

We perform simulations of the neuropeptide Met-enkephalin by using the all-atom ECEPP/3 force field and evaluate the partition function zeros in the complex temperature plane for this continuous energy model by using Simple Molecular Mechanics for Protein (SMMP) and Wang-Landau sampling method. Through massive computation, the density of states and partition function Z(T) as a function of continuos T are obtained for the neuropeptide Met-enkephalin. From the continuous partition function Z(T), the first zero of Met-enkephalin, 3.55728, is evaluated for the first time by using Wang-Landau sampling method. From both the specific heat and the partition function zeros, the conformational transition temperature T = 396.444 Kelvin is obtained for the neuropeptide Met-enkephalin. The transition temperature of the neuropeptide Met-enkephalin is in good agreement with previous results. 왕란다우 표본잡기 서브루틴을 개발하여 추가한 전원자 펩타이드 (all-atom peptide) 시뮬레이션 프로그램인 SMMP (Simple Molecular Mechanics for Protein)와 ECEPP/3 포텐셜을 이용하여 연속에너지 모형인 신경 펩타이드 (neuropeptide) \textit{Met-enkephalin}의 분배함수의 근들을 복소수 온도 평면에서 계산하였다. 시뮬레이션으로부터 얻은 신경 펩타이드 \textit{Met-enkephalin}의 상태밀도와 연속온도의 함수로서의 분배함수 Z(\emph{T})로부터 분배함수의 첫 번째근 3.55782를 왕란다우 표분잡기 방법으로 최초로 계산하였다. 분배함수의 첫 번째 근 3.55782로부터 얻은 신경 펩타이드 Met-enkephalin의 상태전이점 \emph{T} = 396.444 Kevin은 비열로부터 얻은 상태전이점과 일치하였고, 이전의 다른 시뮬레이션 방법들로 수행되었던 신경 펩타이드 \textit{Met-enkephalin} 계산결과와도 매우 잘 일치함을 보였다.

Reliability of Using a Joint Density of States Reconstructed with a Histogram

류설,곽우섭 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.4

We perform simulations of the two dimensional Ising model on a square lattice by using the Wang-Landau sampling method with two different transition probabilities and obtain two kinds of joint densities of states <i>g</i>(<i>E,M</i>): one is exact and the other is reconstructed with a histogram <i>H_R</i>(<i>E,M</i>). We compare the thermodynamic quantities estimated by using the two different joint densities of states, and observe that they become different as the temperature is decreased.

An Efficient Determination of the Critical Temperature of the Blume-Capel Model

류설,곽우섭 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.6

We determinte the critical temperature of the spin-1 Blume-Capel (BC) model by using the derivative of the free energy with respect to the crystal field and call this quantity the “preference” parameter. We carry out simulations of the BC model on a two-dimensional square lattice by using the Wang-Landau sampling method. We measure the susceptibility and the critical temperature of the BC model by using the preference parameter and compare them with those obtained by using the magnetization. We find that the preference parameter works well for the BC model and improves the simulation performance.

금속 나노 입자의 광학적 성질 이해를 위한 유전율 함수의 가상 모델

류설 조선대학교 기초과학연구원 2009 조선자연과학논문집 Vol.2 No.2