• Bulletin of the Korean Chemical Society
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• 제25권5호
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• pp.704-710
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• 2004

A poly(1-hexyl-3,4-dimethyl-2,5-pyrrolylene) (PHDP) was prepared and its luminescence in tetrahydrofuran (THF) was studied. When PHDP is excited by UV light, it produces very strong blue luminescence. The quantum yield of PHDP (Q = 36.9%) is much greater than that of the monomer, 1-hexyl-3,4-dimethylpyrrole (HDP) with Q = 0.61%. The principal luminescence of PHDP has a single decay component with ca. 1 ns, whereas the decay of HDP is complicated. The molecular structure and conformational behavior of HDP and the oligomers up to trimer have been also determined by ab initio Hartree-Fock (HF/6-31$G^{**}$), density functional theory (DFT-B3LYP/6-31$G^{**}$), and semiempirical (ZINDO) methods. According to the results of calculations, it is proposed that the enhanced quantum yield of the polymer PHDP results mostly from the ${\pi}$-conjugation between neighboring pyrrole rings.

• 대한화학회지
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• 제56권4호
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• pp.406-415
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• 2012

The corrosion inhibition of copper-nickel alloy by Ethylenediamine (EDA) and Diethylenetriamine (DETA) in 1.5M HCl has been investigated by weight loss technique at different temperatures. Maximum value of inhibitor efficiency was 75% at $35^{\circ}C$ and 0.2 M inhibitor concentration EDA, while the lower value was 4% at $35^{\circ}C$ and 0.01 M inhibitor concentration DETA. Two mathematical models were used to represent the corrosion rate data, second order polynomial model and exponential model respectively. Nonlinear regression analysis showed that the first model was better than the second model with high correlation coefficient. The reactivity of studied inhibitors was analyzed through theoretical calculations based on density functional theory (DFT). The results showed that the reactive sites were located on the nitrogen (N1, N2 and N4) atoms.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.271-271
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• 2010

Using ab initio density functional theory, we investigate the dimerization and one-dimensional (1-D) polymerization of metal-encapsulated gold nanoclusters, M@$Au_{12}$ (M=W, Mo) and their structural and electronic properties. M@$Au_{12}$ clusters with a magic number 13 can form icosahedral and cuboctahedral structures. We consider various dimer configurations with different compounds and symmetries to find the most stable dimer structure in each case. Au atoms in the one cluster, which participate directly in dimerization, tend to form triangular bonds together with counterpart Au atoms in the other. It is found that both M@$Au_{12}$ and M@$Au_{12}$ clusters are stabilized by about 3 eV due to dimerization. We also calculate and compare the electronic and magnetic properties of different dimerized clusters. Based on our investigation on dimerization, we further study on 1-D polymerization of M@$Au_{12}$ with different compounds and symmetries. We will also discuss their formation energies as well as their electronic and magnetic properties.

• EDISON SW 활용 경진대회 논문집
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• 제3회(2014년)
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• pp.439-441
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• 2014

단층 $MoS_2$는 현재 트랜지스터나 LED등에 활용을 연구중인 물질이다. 단층 $MoS_2$의 밴드구조는 약 1.8eV의 직접 밴드갭을 보이는 반도체로 알려져있다. 이 물질을 소자에 활용할 때 고유의 1.8 eV 직접 밴드갭을 이용한다. 다양한 분야에 소자로 응용되기 위해서는 밴드갭을 조절이 필요하다. 그래서 $MoS_2$의 밴드갭을 조절하는 연구가 행해져 왔는데 그 중 하나가 수소흡착 방법이다. 수소를 단층 $MoS_2$에 흡착시키면 금속 밴드구조를 보인다고 알려져 있다. 본 연구에서는 DFT (Density Functional Theory) 계산을 통하여 밴드갭을 조절하는 다른 방법 중에 하나인 역학적인 힘에 의해 전기적인 특성의 변화에 대한 기초연구를 진행하였다. 단층 $MoS_2$에 in-plane 방향으로 isotropic strain을 주었을 때 밴드갭이 0.68 eV에서 1.89 eV까지 변하는 것을 확인했다. 우리는 단층 $MoS_2$는 약간의 strain에도 밴드갭크기가 다소 많이 변할 뿐만 아니라 직접 밴드갭이 간접 밴드갭으로 변하는 것을 보였다. 심지어 10%정도 strain을 주면 금속으로 변할 것으로 예상된다. 밴드갭이 변하는 성질을 이용하여 센서등 여러 어플리케이션에 단층 $MoS_2$를 활용할 수 있을 것으로 예상된다.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2016년도 추계학술대회 논문집
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• pp.97-97
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• 2016

Development of advanced Li-ion battery cells with high durability is critical for safe operation, especially in applications to electric vehicles and portable electronic devices. Understanding fundamental mechanism on the formation of a solid-electrolyte interphase (SEI) layer, which plays a substantial role in the electrochemical stability of the Li-ion battery, in a cathode was rarely reported unlike in an anode. Using first-principles density functional theory (DFT) calculations and ab-initio molecular dynamic (AIMD) simulations we demonstrate atomic-level process on the generation of the SEI layer at the interface of a carbonate-based electrolyte and a spinel $LiMn_2O_4$ cathode. To accomplish the object we calculate the energy band alignment between the work function of the cathode and frontier orbitals of the electrolyte. We figure out that a proton abstraction from the carbonate-based electrolyte is a critical step for the initiation of an SEI layer formation. Our results can provide a design concept for stable Li-ion batteries by optimizing electrolytes to form proper SEI layers.

• Bulletin of the Korean Chemical Society
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• 제33권11호
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• pp.3719-3726
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• 2012

Formation of Z-DNA, a left-handed double helix, from B-DNA, the canonical right-handed double helix, occurs during important biological processes such as gene expression and DNA transcription. Such B-Z transitions can also be induced by high salt concentration in vitro, but the changes in the relative stability of B-DNA and Z-DNA with salt concentration have not been fully explained despite numerous attempts. For example, electrostatic effects alone could not account for salt-induced B-Z transitions in previous studies. In this paper, we propose that the B-Z transition can be explained if counterion entropy is considered along with the electrostatic interactions. This can be achieved by conducting all-atom, explicit-solvent MD simulations followed by MM-PBSA and molecular DFT calculations. Our MD simulations show that counterions tend to bind at specific sites in B-DNA and Z-DNA, and that more ions cluster near Z-DNA than near B-DNA. Moreover, the difference in counterion ordering near B-DNA and Z-DNA is larger at a low salt concentration than at a high concentration. The results imply that the exclusion of counterions by Z-DNA-binding proteins may facilitate Z-DNA formation under physiological conditions.

• Bulletin of the Korean Chemical Society
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• 제30권2호
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• pp.423-428
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• 2009

The comparative study of three calix[4]heterocycles (calix[4]pyrrole, calix[4]furan, and calix[4]thiophene) has been theoretically performed by using high-level density functional theory (DFT) at the MPWB1K/6-311G$^{**}$//B3LYP/6- 311G$^{**}$ level. The effect of different hetero-atoms (nitrogen, oxygen, and sulfur) placed in the heterocycles on the conformational flexibility, thermodynamic stability order, cavity sizes, charge distributions, and binding propensities are examined. The thermodynamic stability differences between the conformers are found to be much greater in calix[4]pyrrole compared to those in calix[4]furan and calix[4]thiophene. Relatively larger NH group and higher dipole of a pyrrole ring in calix[4]pyrrole contribute to the higher energy barrier for the conformational conversions and relatively rigid potential energy surface compared to the case of calix[4]furan and calix[4]thiophene. The computational results herein provide theoretical understanding of the conformational flexibility and the thermodynamic nature which can be applied to understand the complexation behavior of the three calix[4]heterocycles.

• Bulletin of the Korean Chemical Society
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• 제30권6호
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• pp.1257-1261
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• 2009

We present the theoretical and experimental results of $^{31}P$ NMR and low energy CID MS/MS study of $Hg^{2+}$ binding to fenitrothion (FN). The calculated $^{31}P$ NMR chemical shifts order for FN with $Hg^{2+}$ complex is in good agreement with experimental $^{31}P$ NMR chemical shifts order. The experimental and theoretical $^{31}P$ NMR study of organophosphorus pesticide with $Hg^{2+}$ gives to important information for organophosphorus pesticide metal complexes. ESI-MS and low energy CID MS/MS experiments of $Hg^{2+}$-FN complexes combined with accurate mass measurements give insight into the metal localization and allow unambiguous identification of fragments and hydrolysis products.

• Bulletin of the Korean Chemical Society
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• 제30권5호
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• pp.1021-1025
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• 2009

A novel supramolecular network containing binuclear copper unit $[Cu(phen)_{2}({\mu}-ID\;A)Cu(phen){\cdot}(NO_{3})](NO_{3}){\cdot}4(H_{2}O)$ (1) was synthesized through the self-assembly of iminodiacetic acid ($H_2IDA$) and 1,10-phenanthroline (phen) in the condition of pH = 6. It has been characterized by the infrared (IR) spectroscopy, elemental analysis, single crystal X-ray diffraction, and thermogravimetric analysis (TGA). 1 shows a 2-D supramolecular structure assembled through strong and unique $\pi-\pi$ packing interactions. Density functional theory (DFT) calculations show that theoretical optimized structures can well reproduce the experimental structure. The TGA and powder X-ray diffraction (PXRD) curves indicate that the complex 1 can maintain the structural integrity even at the loss of free water molecules. The magnetic property is also reported in this paper.

• Bulletin of the Korean Chemical Society
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• 제30권7호
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• pp.1573-1578
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• 2009

A computational study of the reactions between Zn-containing species, the products of the thermal decomposition of diethylzinc (DEZn) and water was investigated. The Zn-containing species – $C_2H_5)_2,\;HZnC_2H_5,\;and\;(ZnC_2H_5)_2$ – were assumed to react with water during ZnO metal organic chemical vapor deposition (MOCVD). Density functional theory (DFT) calculations at the level of B3LYP/6-311G(d) were employed for the geometry optimization and thermodynamic property evaluation. As a result dihydroxozinc, $Zn(OH)_2$, was the most probable reaction product common for all three Zn-containing species. A further clustering of $Zn(OH)_2$ was investigated to understand the initial stage of ZnO film deposition. In experiments, the reactions of DEZn and water were examined by in-situ Raman scattering in a specially designed MOCVD reactor. Although direct evidence of $Zn(OH)_2$ was not observed, some relevant reaction intermediates were successfully detected to support the validity of the gas phase reaction pathways proposed in the computational study.