• 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.

• 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.

• Transactions of the Korean hydrogen and new energy society
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• v.25 no.3
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• pp.234-239
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• 2014

To study catalytic activity and hydrogen embrittlement of Pd, Pt, Ni, and Cr in fuel cell electrode, we used density-functional theory. The calculation tools based electron density give much shorter calculation time and cheap costs. Maximum of bond overlap populations of each metal are 0.6539eV for Pd-H, 0.6711eV for Pt-H, 0.6323eV for Ni-H, 0.6152eV for Cr-H. Electron density of Cr has strongest in related metals, which shows strong localization of electron, implying anti hydrogen embrittlement behaviors.

• 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 Chemical Society
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• v.53 no.3
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• pp.257-265
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• 2009

The structures and metal affinities of the binding configurations of $Cu^{+}$ and $Cu^{2+}$ to proline have been investigated using the hybrid three-parameter Density Functional Theory(DFT/B3LYP). We found that the metal-proline bonding and the energy ordering of several conformers were very different in $Cu^{+}$-proline and $Cu^{2+}$-proline. For $Cu^{+}$-proline, the ground state structure was found to have a bidentated coordination in which $Cu^{+}$ was coordinated to the carbonyl oxygen and imino group nitrogen of neutral proline. On the contrary, the ground state structure of $Cu^{2+}$-proline involves chelation between the two oxygens of the carboxylate group in a zwitterionic proline. The metal ion affinity of proline of the most stable $Cu^{+}$-proline complex was calculated as 76.0 kcal/mol at 6-311++G(d,p) level, whereas the $Cu^{2+}$ ion affinity of proline was calculated as 258.5 kcal/mol.

• Journal of Wetlands Research
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• v.20 no.3
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• pp.263-271
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• 2018

In this study, we analyzed the removal efficiency of ammonia nitrogen and phosphate dependant on the column depths using various absorbents such as zeolite silica sand, and activated carbon through the column test. In addition, we analyzed electrochemical adsorption behaviors of ammonia nitrogen and phosphate through the quantum mechanical calculation based on density functional theory calculation. Experimental results represent the removal efficiency of ammonia nitrogen and phosphate are zeolite > activated carbon > silica sand, and activated carbon > zeolite > silica sand, respectively. Zeolite shows high adsorption property for ammonia nitrogen over 90%, regardless of the column depth, while activated carbon exhibits high adsorption property for both ammonia nitrogen and phosphate as the column depth for filter media increases. Theoretical findings using DFT calculation for the adsorption behaviors of adsorbents (activated carbon and silica sand) and nutrients ($PO_4{^{3-}}$, $NH_4{^{+}}$) show that activated carbon represented narrower HOMO-LUMO band gap with high adsorption energy, and even more favorable environment for electron adsorption than silica sand, which leads to the effective removal of nutrients.

• Korean Journal of Mathematics
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• v.19 no.3
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• pp.243-253
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• 2011

We would like to propose a Cooley-Tukey modied algorithm in fast Fourier transform(FFT). Of course, this is a kind of Cooley-Tukey twiddle factor algorithm and we focused on the choice of integers. The proposed algorithm is better than existing ones in speeding up the calculation of the FFT.

• Bulletin of the Korean Chemical Society
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• v.26 no.4
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• pp.589-593
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• 2005

The solvation free energy of proton in methanol was calculated by B3LYP flavor of density functional calculations in combination with the Poisson-Boltzmann continuum solvation model. In order to check the adequacy of the computation level, the free energies of clustering in the gas phase were compared with the experimental data. The solvents were taken into account in a hybrid manner, i.e. one to five molecules of methanol were explicitly considered while other solvent molecules were represented with an implicit solvation model.

• Proceeding of EDISON Challenge
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• 2014.03a
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• pp.430-433
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• 2014

Perovskite 구조를 가진 코발트 산화물 $SrCoO_3$와 Brownmillerite 구조인 $SrCoO_{2.5}$의 electronic structure를 제1원리 계산을 통해 분석하였다. 이들의 magnetic structure를 계산하여 실험을 통해 알려진 값과 비교하였고, 각 구조에서 코발트 이온이 갖는 spin state를 확인할 수 있었다. 코발트 이온은 $SrCoO_3$에서 intermediate spin state(IS)를, $SrCoO_{2.5}$에서는 high spin state(HS)를 갖는데 이것이 lattice constant의 차이에 의한 것인지, 아니라면 차이의 원인은 무엇인지 density of state를 분석함으로써 알아보았다.

• Bulletin of the Korean Chemical Society
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• v.29 no.1
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• pp.69-75
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• 2008

Tautomerism of pyrimidine base cytosine has been comparatively examined on nanoparticle and roughened plate surfaces of silver, gold, and copper by surface-enhanced Raman scattering (SERS). The SERS spectrum was found to be different depending on the metals and their substrate conditions suggesting the dissimilar population of various tautomers of cytosine on the surfaces. The ab initio calculations were performed at the levels of B3LYP, HF, and MP2 levels of theory with the LanL2DZ basis set to estimate the energetic stability of the tautomers with the metal complexes as well as the gas phase state. The amino group and N3-coordinated tautomer was predicted to be more favorable for bonding to Au, whereas the hydroxyl and N1-coordinated zwitter ionic form is most stable with Ag and Cu as a bidentate form from the DFT calculation. The binding energy with the Ag atom is calculated to be smaller than those with the Au and Cu atoms in line with the temperature-dependent SERS spectra of cytosine.