• Bulletin of the Korean Chemical Society
• /
• v.23 no.2
• /
• pp.215-220
• /
• 2002

The structures of 1-fluorosilatrane and the silatranyl cation were calculated by Hartree-Fock (HF), Mofller-Plesset second order (MP2), and various density functional theory (DFT) methods using many different basis sets, demonstrating that the Si-N bonds in two species are quite different. The N${\rightarrow}$Si bond distance of 1-fluorosilatrane from the hybrid DFT calculations $({\sim}2.32{\AA})$ using the Perdew-Wang correlation functional agrees with the gas phase experimental value $(2.324{\AA})$, while other functionals yield larger distances. The MP2 bond distance (2.287${\AA}$ with 6-311$G^{\ast}$) is shorter, and the HF one (2.544 ${\AA}$ with 6-311$G^{\ast}$) larger than those of DFT calculations. The MP2 bond distance is in good agreement with experiment indicating that the electron correlations are crucial for the correct description of the N${\rightarrow}$Si interaction. The silatranyl cation is a stable local minimum on the potential energy surface in all methods employed suggesting that the cation could be a reaction intermediate. The Si-N bond length for the cation is about 1.87 ${\AA}$ for all calculations tested implying that the Si-N bond is mainly conventional. Bonding characteristics of the Si-N bond in two species derived from the natural bond orbital analysis support the above argument based on calculated bond lengths.

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

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2004.11a
• /
• pp.218-221
• /
• 2004

The electronic state of ZnO doped with Al, Ga and In, which belong to III family elements in periodic table, was calculated using the density functional theory. In this study, the program used for the calculation on theoretical structures of ZnO and doped ZnO was Vienna Ab-initio Simulation Package (VASP), which is a sort of pseudo potential method. The detail of electronic structure was obtained by the describe variational $X{\alpha}(DV-X{\alpha})$(DV-Xa) method, which is a sort of molecular orbital full potential method. The optimized crystal structures obtained by calculations were compared to the measured structure. The density of state and energy levels of dopant elements was shown and discussed in association with properties.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.180.2-180.2
• /
• 2014

Opening a bandgap by forming graphene nanoribbons (GNRs) and tailoring their properties via doping is a promising direction to achieve graphene-based advanced electronic devices. Applying a first-principles computational approach combining density functional theory (DFT) and DFT-based non-equilibrium Green's function (NEGF) calculation, we herein study the structural, electronic, and charge transport properties of boron-nitrogen binary edge doped GNRs and show that it can achieve novel doping effects that are absent for the single B or N doping. For the armchair GNRs, we find that the B-N edge co-doping almost perfectly recovers the conductance of pristine GNRs. For the zigzag GNRs, it is found to support spatially and energetically spin-polarized currents in the absence of magnetic electrodes or external gate fields: The spin-up (spin-down) currents along the B-N undoped edge and in the valence (conduction) band edge region. This may lead to a novel scheme of graphene band engineering and benefit the design of graphene-based spintronic devices.

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

• Journal of the Korean Chemical Society
• /
• v.59 no.5
• /
• pp.387-396
• /
• 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
• /
• v.59 no.2
• /
• pp.117-124
• /
• 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 Mineralogical Society of Korea
• /
• v.30 no.2
• /
• pp.59-70
• /
• 2017

$SiO_2$ is one of the most abundant constituents of the Earth's crust and mantle. Probing its electronic structures at high pressures is essential to understand their elastic and thermodynamic properties in the Earth's interior. The in situ high-pressure x-ray Raman scattering (XRS) experiment has been effective in providing detailed bonding transitions of the low-z materials under extreme compression. However, the relationship between the local atomic structures and XRS features at high pressure has not been fully established. The ab initio calculations have been used to overcome such experimental difficulties. Here we report the partial density of states (PDOS) of O atoms and the O K-edge XRS spectra of ${\alpha}-quartz$, ${\alpha}-cristobalite$, and $CaCl_2$-type $SiO_2$ phases calculated using ab initio calculations based on the full-potential linearized augmented plane wave (FP-LAPW) method. The unoccupied O PDOSs of the $CaCl_2$-type $SiO_2$ calculated with and without applying the core-hole effects present significantly distinctive features. The unoccupied O p states of the ${\alpha}-quartz$, ${\alpha}-cristobalite$ and $CaCl_2$-type $SiO_2$ calculated with considering the core-hole effect present similar features to their calculated O K-edge XRS spectra. This confirms that characteristic features in the O K-edge XRS stem from the electronic transition from 1s to unoccupied 2p states. The current results indicate that the core-hole effects should be taken in to consideration to calculate the precise O K-edge XRS features of the $SiO_2$ polymorphs at high pressure. Furthermore, we also calculated O K-edge XRS spectrum for $CaCl_2$-type $SiO_2$ at ~63 GPa. As the experimental spectra for these high pressure phases are not currently available, the current results for the $CaCl_2$-type $SiO_2$ provide useful prospect to predict in situ high-pressure XRS spectra.

• Journal of the Korean Chemical Society
• /
• v.67 no.5
• /
• pp.333-338
• /
• 2023

In this study, the H₂O reaction with SiO clusters was investigated using ab initio Monte Carlo simulations and density functional theory calculations. Three chemistry models, PBE1/DGDZVP (Model 1), PBE1/DGDZVP (Si atom), and aug-cc-pVDZ (O and H atoms), (Model 2) and PBE1/aug-cc-pVDZ (Model 3), were used. The average bond lengths, as well as the relative and reaction energies, were calculated using Models 1, 2, and 3. The average bond lengths of Si-O and O-H are 1.67-1.75 Å and 0.96-0.97 Å, respectively, using Models 1, 2, and 3. The most stable structures were formed by the H transfer from an H₂O molecule except for Si₃O₃-H₂O-1 cluster. The Si₃O₃ cluster with H₂O exhibited the lowest reaction energy. In addition, the Bader charge distributions of the Si_nO_n and (SiO)_n-H₂O clusters with n = 1-7 were calculated using Model 1. We determined that the reaction sites between H₂O and the SiO clusters possessed the highest fraction of electrons.

• Korean Journal of Materials Research
• /
• v.17 no.12
• /
• pp.637-641
• /
• 2007

The total energy and strength of Mg alloy doped with Al, Ca and Zn, were calculated using the density functional theory. The calculations was performed by two programs; the discrete variational $X{\alpha}\;(DV-X{\alpha})$ method, which is a sort of molecular orbital full potential method; Vienna Ab-initio Simulation Package (VASP), which is a sort of pseudo potential method. The fundamental mixed orbital structure in each energy level near the Fermi level was investigated with simple model using $DV-X{\alpha}$. The optimized crystal structures calculated by VASP were compared to the measured structure. The density of state and the energy levels of dopant elements was discussed in association with properties. When the lattice parameter obtained from this study was compared, it was slightly different from the theoretical value but it was similar to Mk, and we obtained the reliability of data. A parameter Mk obtained by the $DV-X{\alpha}$ method was proportional to electronegativity and inversely proportional to ionic radii. We can predict the mechanical properties because $\Delta{\overline{Mk}}$is proportional to hardness.