• Analytical Science and Technology
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• v.20 no.1
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• pp.61-69
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• 2007

The geometrical parameters, total and relative energies, vibrational frequencies, the HOMO-LUMO energy gap, and reorganization energies for the neutral molecule, anion, and cation of $C_{16}H_{16}O_3$ have been determined using density functional method (DFT). The highest level of theory employed in this study is $B3LYP/6-311G^{**}$. Harmonic vibrational frequencies were determined at the $B3LYP/6-311G^{**}$ level of theory. All positive vibrational frequencies were obtained to confirm minimum structures. The HOMO-LUMO energy gap and reorganization energies were calculated to predict the charge transport property of liquid-crystal.

• Proceedings of the KIPE Conference
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• 2016.07a
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• pp.433-434
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• 2016

전력계통은 안정된 전압과 주파수의 전력수급이 요구되는 가운데 발전기의 안정성은 주요 요소이다. 그런데 수차발전기 운전 중 부하 탈락 시 급격한 주파수 상승에 의한 발전기 과전압발생은 발전기 여자시스템의 제어신호인 전압실효값 오차에 기인한 것이다. 이런 오차를 최소화하고 발전기 전압을 안정시키기 위해 ZCP(Zero Crossing Point)와 FPGA를 이용한 주파수 검출영역 확장과 DFT(Discrete Fourier Transform) 알고리즘을 이용하여 안정된 전압실효값을 계산하는 기법을 설계하였다. 실험결과, 기존 57~63Hz 주파수 영역의 DFT 대비 확장된 30~90Hz 대역의 전압실효값 오차는 최대 24.68%에서 0.22%로 대폭 개선되었다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.4A
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• pp.307-314
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• 2010

In this paper, a receive diversity combining technique is proposed for single-carrier frequency division multiple access (SC-FDMA)-based cooperative relay systems when discrete Fourier transform (DFT) spreading sizes for mobile station (MS) and relay station (RS) are different. The proposed technique is composed of a DFT spreading size adjustment block, a phase rotation compensation block, a channel phase compensation block, and a receive diversity combining block. The proposed technique is robust to multipath channels and can be operated with a relatively small computational complexity because receive diversity combining is performed with scalar operations in the frequency-domain. It is shown by computer simulation that the proposed receive diversity combining techniques achieve a performance gain over the conventional maximal ratio combining (MRC) techniques for SC-FDMA-based cooperative relay systems.

• Journal of the Korean Chemical Society
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• v.50 no.4
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• pp.291-297
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• 2006

The equilibrium structures, relative energies and NBO analyses for the possible conformations and transition states which can exist on the internal rotation of CPDFB and CPCFB molecules have been investigated using DFT and ab initio methods with various basis sets. The interaction between bonding orbital ((C1-C3, C2-C3)) and antibonding orbital (n*(B9) and *(B9-Cl11)) was the main characteristic hyperconjugation in both molecules. In addition, the stabilization energy of CPDFB was 6.63kcal/mol and that of CPCFB was 6.97(E-form)/6.79(Z-form) kcal/mol for each conformation. The rotational barriers by internal rotation of BF2- and BFCl- functional groups were evaluated to be 5.3~6.7kcal/mol and 5.7~6.5kcal/mol respectively, which showed good agreement with the experimental values reported by previous dynamic NMR study. Finally, Z-form was more stable than E-form by 0.2 kcal/mol in CPCFB molecule and therefore Z-form was confirmed as global minimum.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.5
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• pp.1045-1057
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• 1997

In this paper, we propose an algorithm of block synchronization that uses data withoug synchronization preambles. Block synchronization systems is implemented using the DSP chip employing the proposed algorithm. The data spread of the DFT blocks is proportional to the offset of DFT block and this information is used to achieve the block synchronization in the receiver. The initial bleock synchronization and the clock synchronization between transmitter and receiver are achieved using the early-late removal of the guard interval. The hardware implmentation is carried out using the DSP chip TM320C30 to verify the proposed block synchronization algorithm with the data rate 1200bps. The DSP chip calculates the spread of the 128 complex FFT in the receiver with the system clock 30MHz. It is believed that the proposed synchronization algorithm can be used in the design of OFDM block synchronization with the high processing DSP chip.

• Korean Chemical Engineering Research
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• v.55 no.5
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• pp.704-710
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• 2017

Although the desalination technique using gas hydrate formation is at a development stage compared to the commercially well-established reverse osmosis (RO), it still draws attention because of its simplicity and moderate operational conditions especially when using refrigerants for guest gases. In this study, DFT (density functional theory)-based molecular modeling was employed to explain the energetics of the gas hydrate formation using HFC (hydrofluorocarbon) and HCFC (hydrochlorofluorocarbon) refrigerants. For guest gases, R-134a, R-227ea, R-236fa, and R-141b were selected and three cavity structures ($5^{12}$, $5^{12}6^2$, and $5^{12}6^4$) composed of water molecules were constructed. The geometries of guest gas, cavity, and cavity encapsulating guest gas were optimized by molecular modeling respectively and their located energies were then used for the calculation of binding energy between the guest gas and cavity. Finally, the comparison of binding energies was used to propose which refrigerant is more favorable for the gas hydrate formation energetically. In conclusion, R-236fa was the best choice in terms of thermodynamic spontaneity, less toxicity, and low solubility in water.

• Journal of the Korean Chemical Society
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• v.59 no.5
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• pp.387-396
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• 2015

The DFT and ab initio calculations have been performed to elucidate hydrogen interaction of HOOO-(H₂O)_n (n=1~5) clusters. The optimized geometries, harmonic vibrational frequencies, and binding energies are predicted at various levels of theory. The trans conformer of HOOO monomer is predicted to be thermodynamically more stable than cis form at the CCSD(T) level of theory. For HOOO-(H₂O)_n clusters, the geometries are optimized at B3LYP/aug-cc-pVTZ and CAM-B3LYP/aug-cc-pVTZ levels of theory. The binding energy of HOOO-H₂O cluster is predicted to be 6.05 kcal/mol at the MP2//CAM-B3LYP/ aug-cc-pVTZ level of theory after zero-point vibrational energy (ZPVE) and basis set superposition error (BSSE) correction. The average binding energy per H₂O is increased according to adding a H₂O moiety in HOOO-(H₂O)_n clusters up to 7.2 kcal/mol for n=5.

• Journal of the Korean Chemical Society
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• v.59 no.2
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• pp.117-124
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• 2015

The DFT and ab initio calculations have been performed to elucidate hydrogen interaction of hydrogen polyoxide dimers, $H_2O_n-H_2O_m$ (n=1-4, m=1-4). The optimized geometries, harmonic vibrational frequencies, and binding energies are predicted at various levels of theory. The harmonic vibrational frequencies of the molecules considered in this study show all real numbers implying true minima. The higher-order correlation effect were discussed to compare MP2 result with CCSD(T) single point energy. The binding energies were corrected for the zero-point vibrational energy (ZPVE) and basis set superposition errors (BSSE). The largest binding energy predicted at the CCSD(T)/cc-pVTZ level of theory is 8.18 kcal/mol for $H_2O_4-H_2O_3$ and the binding energy of water dimer is predicted to be 3.00 kcal/mol.

• Journal of the Korean Chemical Society
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• v.61 no.6
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• pp.328-338
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• 2017

The density functional theory(DFT) and ab initio calculations have been applied to investigate hydrogen interaction of $H_2O_3(H_2O)_n$ clusters(n=1-5). The structures, IR spectra, and H-bonding energies are calculated at various levels of theory. The $trans-H_2O_3$ monomer is predicted to be thermodynamically more stable than cis form at the CCSD(T)/cc-pVTZ level of theory. For clusters, the geometries are optimized at the MP2/cc-pVTZ level of theory. The binding energy of $H_2O_3-H_2O$ cluster is predicted to be -6.39 kcal/mol at the CCSD(T)//MP2/cc-pVTZ level of theory after zero-point vibrational energy (ZPVE) and basis set superposition error (BSSE) correction. This result implies that $H_2O_3$ is a stronger proton donor(acid) than either $H_2O$ or $H_2O_2$. The average binding energies per $H_2O$ are predicted to be 8.25 kcal/mol for n=2, 7.22 kcal/mol for n=3, 8.50 kcal/mol for n=4, and 8.16 kcal/mol for n=5.

• Proceeding of EDISON Challenge
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• 2015.03a
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• pp.300-303
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• 2015

GaSe Single tetralayer의 $4{\times}4$ supercell을 사용하여 alkali metal (Li, Na)의 안정한 흡착 위치를 계산하였다. 가능한 흡착 위치로써 hollow, on top of Se, on top of Ga, Ga-Se bridge, Se-Se bridge를 조사하였다. 위치에 따른 흡착 에너지를 DFT 계산을 통해 얻었고, 계산 값을 통해 가장 안정한 위치를 선정하였다. 그 결과 하나의 원자가 흡착 될 때의 가장 안정한 위치는 hollow 위치이고, bridge 위치는 불안정하다는 것을 알 수 있었다. 또한 가장 안정한 hollow 위치에 두 개의 원자를 거리를 변화시키며 흡착 시켜 계산한 결과, 가장 가깝게 흡착 되었을 때 가장 안정했고 이때 tetralayer의 구조 변형이 두드러짐을 알 수 있었다.