• Bulletin of the Korean Chemical Society
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• v.20 no.10
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• pp.1177-1180
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• 1999

The ab initio SCF MO and density functional theory (DFT) studies are carried out on the electrophilic (1a) and electron transfer (1b) addition reactions to the vinyl double bond of aryl vinyl sulfides and ethers. In the electrophilic addition processes, a double bond shift from C3 = C4 to X = C3 occurs with occupation number (1.97) close to the normal two. Due to this shift direct conjugation between the cationic center, X = S or O, and the para electron-donor substituent becomes impossible so that the reaction energies (or log K) are correlated with σ rather than σ+. By contrast, radical cation formation leads to delocalization of the SOMO, a lone-pair πorbital on X, with four major resonance structures in which cationic charge as well as spin density is delocalized over C4 , X and C7 atoms. As a result, partial πbonds are formed over C1 -X and C3 - C4 with occupation numbers (0.82) lower than one. In two of the cannonical structures, III(Ⅹ) and III(X+), direct conjugation between the cationic center, X, and the para substituent is achieved so that a better correlation with σ+ rather than σis obtained. The SCF MO energies at the HF/3-21G* and HF/6-31G* levels lead to very much inferior Hammett correlations in the σ/ σ+ diagnostic criterion. In contrast, the ρvalues evaluated with the DFT energies can give reliable diagnostic distinction between the two addition mechanisms.

• Progress in Superconductivity
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• v.13 no.2
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• pp.85-89
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• 2011

Using the density functional theory and its combination to the dynamical mean field theory (DMFT), we have studied the electronic and magnetic structures of Fe-based superconductors, $AFe_2As_2$ (A=Ca, Sr, Ba). Our results for the electronic structure agree well with existing angle resolved photoemission spectroscopy (ARPES) data. The temperature dependent magnetization has been calculated using DMFT, and the magnetic transition temperatures are reasonably consistent with the experimentally observed trend for three compounds.

• 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.

• Journal of Korean Society of Environmental Engineers
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• v.38 no.5
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• pp.242-248
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• 2016

The overall reaction rate of fuel cell is governed by oxygen reduction reaction (ORR) in the cathode due to its slowest reaction compared to the oxidation of hydrogen in the anode. The ORR efficiency can be readily evaluated by examining the adsorption strength of atomic oxygen on the surface of catalysts (i.e., known as a descriptor) and the adsorption energy can be controlled by transforming the surface geometry of catalysts. In the current study, the effect of the surface geometry of catalysts (i.e., strain effect) on the adsorption strength of atomic oxygen on platinum catalysts was analyzed by using density functional theory (DFT). The optimized lattice constant of Pt ($3.977{\AA}$) was increased and decreased by 1% to apply tensile and compressive strain to the Pt surface. Then the oxygen adsorption strengths on the modified Pt surfaces were compared and the electron charge density of the O-adsorbed Pt surfaces was analyzed. As the interatomic distance increased, the oxygen adsorption strength became stronger and the d-band center of the Pt surface atoms was shifted toward the Fermi level, implying that anti-bonding orbitals were shifted to the conduction band from the valence band (i.e., the anti-bonding between O and Pt was less likely formed). Consequently, enhanced ORR efficiency may be expected if the surface Pt-Pt distance can be reduced by approximately 2~4% compared to the pure Pt owing to the moderately controlled oxygen binding strength for improved ORR.

• Proceedings of the Polymer Society of Korea Conference
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• 2006.10a
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• pp.230-230
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• 2006

Density functional theory (DFT) calculations using the B3LYP hybrid functional and the 6-311++G(d,p) basis set have been performed to predict the wavelength dispersion of optical absorbance and refractive indices for organic compounds and polymers in the range between the vacuum UV (${\sim}157\;nm$) and near-IR (${\sim}850\;nm$). The DFT calculations can reproduce the experimental dispersions of absorbance and refractive indices with high accuracy and low costs. The calculated dispersions demonstrate that the judicious introductions of $-F\;and\;-CF_{3}$ into alicyclic and heterocyclic compounds are effective in reducing the absorption at shorter wavelengths. In addition, the calculated Abbe numbers that represent the refractive index dispersion in the visble region are linearly proportional to the calculated refractive indices at 589 nm.

• Bulletin of the Korean Chemical Society
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• v.35 no.3
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• pp.770-774
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• 2014

The bond dissociation energy (BDE) of the chemical bond between the carbon and oxygen atoms of a simple TEMPO-derivative is calculated by employing the density functional theory, the $2^{nd}$ order M${\phi}$ller-Plesset (MP2) perturbation theory, and complete basis set (CBS) methods. We find that BDE of the positive ion of the TEMPO-derivative is larger at least by 7 kcal/mol than that of the negative ion, which implies that the dissociation reaction rate of the positive ion should be slower than that of the negative ion. Such theoretical predictions are contrary to the results of our previous experiments (Anal. Chem. 2013, 85, 7044), in which the larger energy was required for negative o-TEMPO-Bz-C(O)-peptides to undergo the dissociation reactions than for the positive ones. By comparing our theoretical results to those of the experiments, we conclude that the dissociation reaction of o-TEMPO-Bz-C(O)-peptide should occur in a complicated fashion with a charge, either positive or negative, probably being located on the amino acid residues of the peptide.

• Bulletin of the Korean Chemical Society
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• v.34 no.10
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• pp.3022-3026
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• 2013

The adsorption of carbon dioxide on graphene sheets was theoretically investigated using density functional theory (DFT) and MP2 calculations. Geometric parameters and adsorption energies were computed at various levels of theory. The $CO_2$ chemisorption energies on graphene-$C_{40}$ assuming high pressure are predicted to be 71.2-72.1 kcal/mol for the lactone systems depending on various C-O orientations at the UCAM-B3LYP level of theory. Physisorption energies of $CO_2$ on graphene were predicted to be 2.1 and 3.3 kcal/mol, respectively, at the single-point $UMP2/6-31G^{**}$ level of theory for perpendicular and parallel orientations.

• Bulletin of the Korean Chemical Society
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• v.31 no.8
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• pp.2416-2418
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• 2010

• Proceeding of EDISON Challenge
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• 2013.04a
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• pp.278-281
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• 2013

We investigate special arrangements of lithium atoms adsorbed on graphene. By changing adsorption sites and increasing number of atoms, adsorption of lithium atoms on ($3{\times}3$) graphene is investigated using the density functional theory (DFT) calculations. In this study, three kinds of adsorption sites are considered, such as top, bridge and hollow sites.

• Journal of the Korean Chemical Society
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• v.67 no.3
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• pp.204-207
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• 2023