• Bulletin of the Korean Chemical Society
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• 제24권6호
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• pp.717-722
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• 2003

The structure, force field and vibrational spectra of triphenylene are studied by $B3LYP/6-31G^*$(5d) level of theory. The results are compared to those of the related system, phenanthrene. The scale factors in nonredundant local coordinates obtained after fitting the DFT frequencies to the experimental numbers of phenanthrene-$d_0 and -d_{10}$ are transferred to predict the spectra and assignment of triphenylene for in-plane modes. The frequencies based on scaling methodology due to Lee et al. are also obtained. These frequencies are compared with the predicted numbers based on scale factors from phenanthrene. Probable assignment for out-of-plane modes is proposed based on simple scaling of Scott and Radom (scale factor 0.9614) as well as by scaling methodology by Lee et al.

• 한국응용과학기술학회지
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• 제22권4호
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• pp.299-305
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• 2005

In this study, we designed color of tunable and high efficient organic materials using the quantum dynamics and the semi-empirical calculation, and applied this results to the fabrication of organic light-emitting diodes. Also we optimized the molecular structure of phosphorescent materials and the energy transfer from a host to a dye which makes organic light-emitting diodes improve. Using quantum dynamics method, the molecular structures of ligand only and the whole metal chelate were optimized, and these energy levels were calculated. From this test results, we could understand the emission mechanism of phosphors with various ligands as well as design the proper ligands reducing the T-T annihilation and the carrier lifetime. We also could design ligands with various colors using this test method.

• Bulletin of the Korean Chemical Society
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• 제32권10호
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• pp.3614-3617
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• 2011

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($4{\times}2$) 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.

• Journal of Magnetics
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• 제14권1호
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• pp.1-6
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• 2009

The magnetic properties of ${Bi_x}{Ca_{1-x}}{MnO_3}$ for x = 0.12, 0.13, 0.14, 0.15, and 0.16 were examined by measuring magnetic susceptibility, resistivity and electron magnetic resonance at different temperatures. ${Bi_x}{Ca_{1-x}}{MnO_3}$ showed complicated magnetic structure that varies with temperature and composition, particularly around Bi composition x. 0.15. The aim of this study was to determine how the magnetic and physical properties of ${Bi_x}{Ca_{1-x}}{MnO_3}$ change in this region. In addition, first principles calculations of the magnetic phase of ${Bi_x}{Ca_{1-x}}{MnO_3}$ for x = 0, 0.125, 0.25 were carried out, and the spin state, electric and magnetic characteristics are discussed.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.136-136
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• 2013

High-resolution photoemission spectroscopy (HRPES) measurements were collected and density functional theory (DFT) calculations were conducted to track the coverage dependent variation of the absorption structure of 2-thiophenecarboxaldehyde (C4H3SCHO: TPCA) on the Ge(100) surface at room temperature. In an effort to identify the most probably adsorption structures on the Ge(100) surface, we deposited TPCA molecules at a low coverage and at a high coverage and compared the differences between the electronic features measured using HRPES. The HRPES data provided three possible adsorption structures of TPCA on the Ge(100) surfaces, and DFT calculations were used to determine the plausibility of the structures. HRPES analysis, corroborated by DFT calculations, indicated that an S-dative bonded structure was the most probable adsorption structure at relatively lower coverage levels, the [4+2] cycloaddition structure was the second most probable structure, and the [2+2]-C=O cycloaddition structure was the last probable structure on the Ge(100) surfaces at relatively higher coverage levels.

• Nano
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• 제13권12호
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• pp.1850138.1-1850138.6
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• 2018

Two-dimensional (2D) or layered materials have a great potential for applications in energy storage, catalysis, optoelectronics and gas separation. Fabricating novel 2D or quasi-2D layered materials composed of relatively abundant and inexpensive atomic species is an important issue for practical usage in industry. Here, we suggest the layer-structured AlOOH (Boehmite) as a promising candidate for such applications. Boehmite is a well-known layer-structured material and a single-layer can be exfoliated from the bulk boehmite by breaking the interlayer hydrogen bonding. We study atomic and electronic band structures of both bulk and single-layer boehmite, and also obtain the single-layer exfoliation energy using first-principles calculations.

• Bulletin of the Korean Chemical Society
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• 제27권7호
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• pp.1048-1052
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• 2006

Ab initio calculations of the structure, atomic charges and natural bond orbital (NBO) have been performed at HF/6-311G** and B3LYP/6-311G** levels for the title compound of dibenzothiazyl-disulfide. The calculated results show that the two nitrogen atoms have the biggest negative charges and they are the potential sites to react with the metallic ions, which make the title compound become a di-dentate ligand. Vibrational frequencies of the title compound have been obtained and compared with the experimental value and the comparison indicates that B3LYP/6-311G** level is better than HF/6-311G** level to predict the vibrational frequencies for the system studied here. For the title compound, electronic absorption spectra calculated by time?ependent density functional theory (TD-DFT) are more accurate than Hartree-Focksingle-excitation CI (CI-Singles) method. NBO analyses show that the electronic transitions are mainly derived from the contribution of bands $\pi\rightarrow\pi^{*}$. Thermodynamic calculated results show that the formation of the title compound from 2-mercaptobenzothiazole is a spontaneous process at room temperature with the change of free Gibbs being negative value.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.169-169
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• 2014

Interfacial electronic structure of bathocuproine and Al was investigated using in-situ photoemission spectroscopy and density functional theory (DFT) calculations. Bathocuproine is used for exciton blocking and electron transport material in organic photovoltaics and Al is typical cathode material. When thin thickness of Al was thermally evaporated on BCP, gap states were observed by ultraviolet photoemission spectroscopy. The closest gap state yielded below 0.3 eV from Fermi level. By x-ray photoemission spectroscopy, interaction of Al with nitrogen of BCP was observed. To understand the origin of gap states, DFT calculation was carried out and gap states was verified with successive calculation of interaction of Al and nitrogen of BCP. Furthermore, emergency of another state above Fermi level was observed. Remarkable reduction of electron injection barrier between Al and BCP, therefore, is possible.

• Bulletin of the Korean Chemical Society
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• 제34권4호
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• pp.1043-1046
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• 2013

Prediction of physicochemical properties of organic molecules is an important process in chemistry and chemical engineering. The MSEP approach developed in our lab calculates the molecular surface electrostatic potential (ESP) on van der Waals (vdW) surfaces of molecules. This approach includes geometry optimization and frequency calculation using hybrid density functional theory, B3LYP, at the 6-31G(d) basis set to find minima on the potential energy surface, and is known to give satisfactory QSPR results for various properties of organic molecules. However, this MSEP method is not applicable to screen large database because geometry optimization and frequency calculation require considerable computing time. To develop a fast but yet reliable approach, we have re-examined our previous work on organic molecules using two semi-empirical methods, AM1 and PM3. This new approach can be an efficient protocol in designing new molecules with improved properties.

• Bulletin of the Korean Chemical Society
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• 제25권1호
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• pp.90-96
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• 2004

The conformations of dicyclopropyl, isopropyl cyclopropyl, and diisopropylcarbenes were optimized using density functional theory (B3LYP/6-31G(d)). We showed that the optimized geometries of carbenes with cyclopropyl groups are fully in accord with those expected for bisected W-shaped conformations, in which the effective hyperconjugation of a cyclopropyl group with singlet carbene can occur. The stabilization energies were evaluated at the B3LYP/6-311+G(3df, 2p)//B3LYP/6-31G(d) + ZPE level using an isodesmic equation. The relative stability of carbenes is in the order $(c-Pr)_2$C: > (i-Pr)(c-Pr)C: > $(i-Pr)_2$C:, and a cyclopropyl group stabilizes carbene more than an isopropyl group by nearly 9 kcal/mol. Energies for the decomposition of diazo compounds to carbenes increase in the order $(c-Pr)_2$ < (i-Pr)(c-Pr) < $(i-Pr)_2$ by ~9 kcal/mol each. From a singlettriplet energy gap ($E_{ST}$) calculation, the singlet level is lower than the triplet level and the $E_{ST}$ shows a trend similar to the stabilization energy calculations. For comparison, the optimized geometries and stabilization energies for the corresponding carbocations were also studied at the same level of calculation. The greater changes in geometries and the higher stabilization energies for carbocations compared to carbenes can explain the greater hyperconjugation effect.