• Korean Chemical Engineering Research
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• v.56 no.6
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• pp.909-913
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• 2018

A hydrocarbon trap (HT) plays an important role of controlling vehicle emissions in the so-called cold emission period by holding hydrocarbons until three way catalysts (TWCs) are thermally activated. In this study, we have investigated the adsorption characteristics of cation (H, La, K, and Ag)-exchanged ZSM-5 zeolites for hydrocarbons (propylene, n-butane, and toluene) by DFT (density functional theory)-based computational chemistry. Cation exchange is to improve the hydrothermal stability of zeolites and their adsorption capacity, thereby rendering cation-exchanged zeolites promising materials for HT. The idea of cluster approximation makes the calculation of adsorption energies superbly efficient in computation. The results showed that Ag-exchanged ZSM-5 would be the best for the adsorption of all three adsorbates, without often encountered Ag oxidation in experiments. Besides, the hydrothermal stability of La-exchanged ZSM-5 was confirmed from the change of geometrical parameters by cation exchange, and it showed good adsorption capacity for propylene and toluene. Hydrogen-exchanged ZSM-5 was also good for hydrogen adsorption, but had poor hydrothermal stability.

• Bulletin of the Korean Chemical Society
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• v.25 no.12
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• pp.1855-1858
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• 2004

Molecular geometries for the cationic and neutral species of OXO (X=Cl, Br, and I) are optimized using the Hartree-Fock (HF) theory, the second order Moller-Plesset perturbation theory (MP2), the density functional theory with the B3LYP hybrid functional (B3LYP), and the coupled cluster theory using single and double excitation with a perturbational treatment of triplet excitation (CCSD[T]) methods, with two basis sets of triple zeta plus polarization quality. The single point calculations for these species are performed at the CCSD(T,Full) level. The harmonic vibrational frequencies for these species are calculated at the HF, MP2, B3LYP and CCSD(T) levels. The adiabatic ionization potential for OIO is calculated to be 936.7 kJ/mol at the CCSD(T,Full) level and the correct value is estimated to be around 945.4 kJ/mol.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.127.1-127.1
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• 2013

Recent experimental evidence that fluorinated graphene creates local magnetic moments around F adatoms has not been supported by semilocal density-functional theory (DFT) calculations where the adsorption of an F adatom induces no magnetic moment in graphene. Here, we show that such an incorrect prediction of the nonmagnetic ground state is due to the self-interaction error inherent in semilocal exchange-correlation functionals. The present hybrid DFT calculation for an F adatom on graphene predicts not only a spin-polarized ground state with a spin moment of ${\sim}1{\mu}_B$, but also a long-range spin polarization caused by the bipartite nature of the graphene lattice as well as the induced spin polarization of the graphene states. The results provide support for the experimental observations of local magnetic moments in fluorinated graphene.

• Corrosion Science and Technology
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• v.21 no.1
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• pp.21-31
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• 2022

Potentiodynamic polarization, EIS measurements, quantum chemical calculations, and molecular dynamic simulations were used to investigate the corrosion behavior of mild steel in 0.5 M aqueous hydrochloric acid medium in the presence or absence of nystatin drug. Potentiodynamic tests suggested that this molecule could act as a mixed inhibitor due to its adsorption on the mild steel surface. The objective of this study was to exploit theoretical calculations to gain a better understanding mechanism of inhibition. Calculating the adsorption behavior of the investigated molecule on Fe (1 1 0) surface was accomplished using Monte Carlo simulation. Molecules were also investigated using Density Functional Theory (DFT), specifically PBE functional, in order to identify the link between molecular structure and corrosion inhibition behavior of the compound under investigation. Adsorption energies between nystatin and iron were estimated more accurately by utilizing Molecular Mechanics calculation with Periodic Boundary Conditions (PBC). Estimated theoretical parameters significantly assisted our understanding of the corrosion inhibition mechanism exhibited by this molecule. They were found to be in accord with experimental results.

• Bulletin of the Korean Chemical Society
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• v.34 no.4
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• pp.1055-1060
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• 2013

The adsorption structures of threonine on the Ge(100) surface were investigated using core-level photoemission spectroscopy (CLPES) in conjunction with density functional theory (DFT) calculations. CLPES measurements were performed to identify the experimentally preferred adsorption structure. The preferred structure indicated the relative reactivities of the carboxyl and hydroxymethyl groups as electron donors to the Ge(100) surface during adsorption. The core-level C 1s, N 1s, and O 1s CLPES spectra indicated that the carboxyl oxygen competed more strongly with the hydroxymethyl oxygen during the adsorption reaction. Three among six possible adsorption structures were identified as energetically favorable using DFT calculation methods that considered the inter- and intra-bonding configurations upon adsorption onto the Ge(100) surface. These structures were O-H dissociated N dative inter bonding, O-H dissociated N dative intra bonding, O-H dissociation bonding. One of the adsorption structures: O-H dissociated N dative inter bonding was predicted to be stable in light of the transition state energies. We thus confirmed that the most favorable adsorption structure is the O-H dissociated N dative-inter bonding structure using CLPES and DFT calculation.

• Korean Chemical Engineering Research
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• v.55 no.2
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• pp.270-274
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• 2017

Formic acid has been known as one of key sources of hydrogen. Among various monometallic catalysts, hydrogen can be efficiently produced on Pd catalyst. However, the catalytic activity of Pd is gradually reduced by the blocking of active sites by CO, which is formed from the unwanted indirect oxidation of formic acid. One of promising solutions to overcome such issue is the design of alloy catalyst by adding other metal into Pd since alloying effect (such as ligand and strain effect) can increase the chance to mitigate CO poisoning issue. In this study, we have investigated formic acid deposition on the bimetallic $Pd/Pd_3Fe$ core-shell nanocatalyst using DFT (density functional theory) calculation. In comparison to Pd catalyst, the activation energy of formic acid dehydrogenation is greatly reduced on $Pd/Pd_3Fe$ catalyst. In order to understand the importance of alloying effects in catalysis, we decoupled the strain effect from ligand effect. We found that both strain effect and ligand effect reduced the binding energy of HCOO by 0.03 eV and 0.29 eV, respectively, compared to the pure Pd case. Our DFT analysis of electronic structure suggested that such decrease of HCOO binding energy is related to the dramatic reduction of density of state near the fermi level.

• Journal of Korean Society of Environmental Engineers
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• v.36 no.6
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• pp.442-450
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• 2014

Concern has grown over a presence of micropollutants in natural water since sulfonamide antibiotic substances such as sulfamethazine, sulfamethoxazole, sulfathiazole have been frequently detected in Nakdong River, Korea. The current work investigates the degradation of the three sulfonamide substances by using quantum chemistry calculations of density functional theory (DFT) and experimental measurement techniques of Fourier transform infrared spectroscopy (FT-IR) and ultraviolet-visible spectrophotometer (UV-VIS). DFT calculations demonstrate that the lowest energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbitals (LUMO) lies in sulfanilamide functional group of sulfonamide, implying that the sulfanilamide functional group would be the most active site for ozone oxidation. Also, UV-VIS spectra and FT-IR analysis reveal that 260 nm band originated from sulfanilamide group was absent after ozone oxidation, indicating that a functional group of amine (N-H) was removed from sulfanilamide. Both theoretical and experimental observations agree well with each other, demonstrating the DFT calculation tool can be an alternative tool for the prediction of chemical reactions in purification treatment processes.

• Current Applied Physics
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• v.18 no.12
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• pp.1507-1512
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• 2018

The development of an organic-based aqueous redox flow battery (RFB) using quinone as an electroactive material has attracted great attention recently. This is because this battery is inexpensive, produces high energy density, and is environment friendly in stationary electrical energy storage applications. Herein, we investigate the redox potentials and solubilities of indole-5,6-quinone and indole-4,7-quinone derivatives in terms of the substituent effects of functional groups using theoretical calculations. Our results indicate that full-site substituted derivatives of indolequinone are more useful as active materials compared to single-site substituted derivatives. In particular, our calculations reveal that the substitution of $-PO_3H_2$ and $-SO_3H$ functional groups with multiple polar bonds is very effective in increasing the activity of the aqueous RFB. As a strategy to overcome the limitation that the aqueous solubility is intrinsically low because they are organic molecules, we suggest the substitution of functional groups with multiple polar bonds to the backbones of active organic materials. Among 180 indolequinone derivatives, 17 candidates that meet the redox potential standards ($${\leq_-}0.2V$$ or $${\geq_-}0.9V$$) and eight candidates with solubility exceeding 2 mol/L are identified. Three indolequinone derivatives that satisfy both conditions are finally presented as promising electroactive candidates for an aqueous RFB.

• Journal of the Korean Magnetic Resonance Society
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• v.16 no.1
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• pp.78-90
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• 2012

To understand the electronic structure of $[NiS_4]^-$ complex ions, two complexes with such $[NiS_4]^-$ core, $FcCH=CHPymCH_3[Ni(dmit)_2]$ (Pym = pyridinium, $dmit^{2-}$ = 2-thioxo-1,3-dithiole-4,5-dithiolate) and $FcCH=CHPymCH_3[Ni(dddt)_2]{\cdot}{\frac{1}{2}}H_2O$ ($dddt^{2-}=5,6-dihydro-1,4-dithiin-2,3-dithiolato$), were synthesized to be characterized by X-ray crystallography, single crystal electron paramagnetic resonance (EPR) and density functional theory (DFT) calculation. Powder EPR spectra show narrow g-anisotropy but the anisotropy is bigger in $[Ni(dmit)_2]^-$ than in $[Ni(dddt)_2]^-$, indicating bigger spin density in Ni(III) d-orbital of $[Ni(dmit)_2]^-$ than in $[Ni(dddt)_2]^-$, which is consistent to DFT results. EPR studies of the crystals of the complexes surprisingly suggest that the $g_y$-axis of $[Ni(dddt)_2]^-$ is approximately on or perpendicular to the $[NiS_4]^-$ plane while the $g_y$-axis of $[Ni(dmit)_2]^-$ is on the plane, though DFT study of the complexes of this study and previously reported $[NiS_4]^-$ complexes indicate that the $g_y$-axis is on the $[NiS_4]^-$ plane.

• Journal of the Korean Magnetics Society
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• v.25 no.4
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• pp.106-110
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• 2015

We have studied electronic and magnetic structure of 2 kinds of diiron molecules using OpenMX method based on density functional method. The calculated density of states of diiron-2 is similar with that of diiron-4 because of equal number of 6 ligand atoms. The calculated total energy with antiferromagnetic spin configuration is lower than those of ferromagnetic configurations for both of them. The exchange interaction J of diiiron-4 between $Fe^{+3}$ atoms is one order larger than that of diiron-2, and the calculated J matches well with the experimental one. That comes from the short distance of Fe-O and the high O 2p energy levels. It derives a strong super exchange interaction. The angle of diiron-4 between Fe atoms is bigger than that of diiron-2. It also derives a strong super exchange interaction because of the ${\sigma}$-bond between Fe and O atoms.