• Journal of the Korean Magnetic Resonance Society
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• v.22 no.4
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• pp.101-106
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• 2018

Magnetite is the oldest magnet material known to mankind. It is getting attention again from solid state physics researchers now a days because it is one of the most strongly correlated electron systems. Spin, charge, and orbital orders are interplaying with lattice and involved in the Verwey transition where magnetization, conductivity, and structure changes suddenly. The peculiar ordering states above and below the transition temperature mainly originate from the coexistence of $Fe^{2+}$ and $Fe^{3+}$ ions in the B site of the inverse spinel structure. In particular, the state of the charge and orbital order was the oldest and most intriguing problem. NMR has made significant contribution to the investigation of this question. A. Abragam stated that there is no doubt that NMR is a very powerful tool for the study of ferromagnetic and antiferromagnetic materials. In this mini-review, a short history of NMR investigation of magnetite is presented, providing a support to Abragam's claim.

• Bulletin of the Korean Chemical Society
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• v.31 no.4
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• pp.781-788
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• 2010

Experimental and theoretical studies show that all covalent azides possess a nonlinear azide group. They also rationalize this remarkable structural feature. We have seen that the most important non-covalent contributions in the covalently bound azides system (X-N1-N2-N3) are the $\pi$-delocalization over the entire molecule and a strong negative hyperconjugation which donates electron density from the filled $\sigma$ (X-N1) orbital into the unfilled, antibonding $\pi^*$ (N2-N3) orbital. For transition metal azide complexes, a bent configuration and a small difference between the N-N bond lengths, generally the longer one being adjacent to the transition metal, were observed.

• Proceedings of the Korean Magnestics Society Conference
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• 2000.09a
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• pp.461-461
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• 2000

We have investigated electronic structuresof antiferromagnetic YBaCo_2O_5 using the local spin-density approximation (LSDA) + U method. The charge and orbital ordered insulating ground state is correctly obtained with the strong on-site Coulomb interaction. Co^{2+} and Co^{3+} ions are found to be in the high spin (HS) and intermediate spin (IS) state, respectively. The tetragonal to orthorhombic structural transition is responsible for the ordering phenomena and the spin states of Co ions. The large contribution of the orbital moment to the total magnetic moment indicates that the effect of the spin-orbit coupling is very important in YBaCo_2O_5.

• Bulletin of the Korean Chemical Society
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• v.22 no.5
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• pp.499-502
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• 2001

Unexpectedly, the brightest row was known to represents the lowest lying Te atoms in the STM image of NbTe2. Projected density of states and crystal orbital overlap population show that the 5pz orbital of the lowest lying Te(2) atom doe s not interact with the 4d orbital of Nb strongly so that the 5pz band remains in the vicinity of the Fermi energy. Consequently the lowest lying Te(2) atoms contribute higher electron density near the Fermi energy which in turn exhibits brightest image in the STM experiments.

• Journal of Magnetics
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• v.13 no.4
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• pp.140-143
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• 2008

The magnetic and structural properties of transition metal (Mn, Fe, Co) monolayers on Ta(001) surfaces are investigated theoretically by using the first principles full-potential linearized augmented plane wave method. Mn and Fe monolayers become ferromagnetic on Ta(001) surfaces while Co monolayers becomes non-magnetic. The paramagnetism of Co monolayers is explained by the Stoner theory of magnetism. The magnetic coupling of a transition metal overlayer with a substrate is ascribed to the orbital hybridization between the s and d orbitals of the transition metal.

• Bulletin of the Korean Chemical Society
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• v.33 no.12
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• pp.4079-4083
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• 2012

The mechanism of the cycloaddition reaction between singlet state dichlorosilylene germylidene ($Cl_2Si=Ge:$) and acetone has been investigated with B3LYP/6-$31G^*$ and B3LYP/6-$31G^{**}$ method, from the potential energy profile, we predict that the reaction has one dominant reaction pathway. The presented rule of the reaction is that the two reactants firstly form a Si-heterocyclic four-membered ring germylene through the [2+2] cycloaddition reaction. Because of the 4p unoccupied orbital of Ge atom in the Si-heterocyclic four-membered ring germylene and the ${\pi}$ orbital of acetone forming a ${\pi}{\rightarrow}p$ donor-acceptor bond, the Si-heterocyclic four-membered ring germylene further combines with acetone to form an intermediate. Because the Ge atom in the intermediate hybridizes to an $sp^3$ hybrid orbital after the transition state, then, the intermediate isomerizes to spiro-heterocyclic ring compound involving Si and Ge (P4) via a transition state.

• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.2028-2030
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• 2005

The electrical conductivity of manganese oxide and complex manganese oxide produced by anodic deposition method was measured. The additive transition metal is Cu, Co and Fe. The transition metals like as Cu, Co and Fe improved electrical conductivity of complex manganese oxide compared with manganese oxide. This is coincide with the results of molecular orbital calculation by DV-Xa.

• Current Optics and Photonics
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• v.1 no.4
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• pp.402-411
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• 2017

Combined LIBS-Raman spectroscopy has been widely studied, due to its complementary capabilities as an elemental analyzer that can acquire signals of atoms, ions, and molecules. In this study, the classification of polymorphs was performed by laser-induced breakdown spectroscopy (LIBS) to overcome the limitation in molecular analysis; the results were verified by Raman spectroscopy. LIBS signals of the $CaCO_3$ polymorphs calcite and aragonite, and $CaSO_4{\cdot}2H_2O$ (gypsum) and $CaSO_4$ (anhydrite), were acquired using a Nd:YAG laser (532 nm, 6 ns). While the molecular study was performed using Raman spectroscopy, LIBS could also provide sufficient key data for classifying samples containing different molecular densities and structures, using the peculiar signal ratio of $5s{\rightarrow}4p$ for the orbital transition of two polymorphs that contain Ca. The basic principle was analyzed by electronic motion in plasma and electronic transition in atoms or ions. The key factors for the classification of polymorphs were the different electron quantities in the unit-cell volume of each sample, and the selection rule in electric-dipole transitions. The present work has extended the capabilities of LIBS in molecular analysis, as well as in atomic and ionic analysis.

• Journal of the Korean Chemical Society
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• v.28 no.4
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• pp.217-230
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• 1984

The MINDO/3 method was used in determination of transition states and activation barriers for various 1,2-, 1,3- and 1,5-sigmatropic hydrogen rearrangements involving systems with central carbon atom. It was found that, besides the consideration of orbital symmetry, steric effect, aromaticity, and orbital interactions were found to dictate the stability of the transition state. For systems with hetero atoms, lone pair orbitals tend to ease orbital distortion required at the transition state by participating in hydrogen transfer process and were found to lower the activation barrier accordingly. Comparison of the relative barrier heights with those obtained by using more sophisticated ab initio MO calculations showed that the MINDO/3 results give qualitatively the same tendency of the relative order of the activation barriers.

• Bulletin of the Korean Chemical Society
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• v.34 no.2
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• pp.453-459
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• 2013

In phtosynthetic light harvesting complexes, the electronic transition energies of chlorophylls are influenced by the Coulombic interaction with nearby molecules. Variation of the interactions caused by structural inhomogeneity in biological environment results in a distribution of disordered electronic transition energies of chlorophylls. In order to provide a practical guide to predict qualitative tendency of such distribution, we model four porphyrin derivatives including chlorophyll a molecule interacting with an external positive charge and calculate their transition energies using the time dependent density functional method. It is found that ${\pi}-{\pi}^*$ transition energies of the molecules are generally blue-shifted by the charge because this stabilizes occupied molecular orbitals to a greater extent than unoccupied ones. Furthermore, new transitions in the visible region emerge as a result of the red-shift in energy of an unoccupied Mg orbital and it is suggested that light-induced electron transfer may occur from the tetrapyrrole ring to the central magnesium when the molecules are interacting with a positive charge.