• Bulletin of the Korean Chemical Society
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• v.26 no.4
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• pp.585-588
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• 2005

Bipyridine and its derivatives have been widely used as the ligands in transition metal complexes. The proton affinities of pyridine derivatives were calculated using an ab initio quantum mechanical method (B3LYP with various double zeta and triple zeta basis sets) in combination with the Poisson-Boltzmann continuum solvation model. Van der Waals radii of the atoms in the heterocyclic rings for the solvation energy calculation were set to values determined to reproduce the $pK_a$ values of guanine and oxoguanine derivatives and that of chlorine was optimized to reproduce the experimental values of relating compounds. The $pK_a$ values for the heterocyclic ring compounds were in agreement with the experimental values with a mean unsigned error of 0.45 $pK_a$ units.

• Bulletin of the Korean Chemical Society
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• v.32 no.2
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• pp.439-443
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• 2011

Using the projection operator technique, a reduced density matrix theory for linear absorption spectrum of energy transfer systems is developed for the theoretical absorption line shape of the systems with non-Condon transitions. As an application, we considered a model system of OH vibrations of water. In the present model calculation, the OH vibration modes are coupled to each other via intra-molecular coupling mechanism while their intermolecular couplings are turned off. The time-correlation functions appearing in the formulation are calculated from a mixed quantum/classical mechanics method. The present theory is successful in reproducing the exact absorption line shape. Also the present theory was improved from an existing approximate theory, time-averaged approximation approach.

• Bulletin of the Korean Chemical Society
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• v.29 no.3
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• pp.679-681
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• 2008

• Bulletin of the Korean Chemical Society
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• v.30 no.7
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• pp.1539-1542
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• 2009

Using one-range addition theorems for Slater type orbitals (STOs) and Coulomb-Yukawa like correlated interaction potentials (CIPs) introduced by the author, the series expansion formulae are derived for the multicenter multielectron integrals. The expansion coefficients occurring in these relations are presented through the overlap integrals of two STOs. The convergence of series expansion relations is tested by calculating concrete cases. The accuracy of the results is quite high for quantum number, screening constants and location of orbitals. The final results are especially useful in the calculation of multielectron properties for atoms and molecules when Hartree-Fock-Roothaan (HFR) and explicitly correlated methods are employed.

• Bulletin of the Korean Chemical Society
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• v.34 no.1
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• pp.179-187
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• 2013

We describe newly developed software named KPACK for relativistic electronic structure computation of molecules containing heavy elements that enables the two-component ab initio calculations in Kramers restricted and unrestricted formalisms in the framework of the relativistic effective core potential (RECP). The spin-orbit coupling as relativistic effect enters into the calculation at the Hartree-Fock (HF) stage and hence, is treated in a variational manner to generate two-component molecular spinors as one-electron wavefunctions for use in the correlated methods. As correlated methods, KPACK currently provides the two-component second-order M${\o}$ller-Plesset perturbation theory (MP2), configuration interaction (CI) and complete-active-space self-consistent field (CASSCF) methods. Test calculations were performed for the ground states of group-14 elements, for which the spin-orbit coupling greatly influences the determination of term symbols. A categorization of three procedures is suggested for the two-component methods on the basis of spin-orbit coupling manifested in the HF level.

• Bulletin of the Korean Chemical Society
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• v.16 no.10
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• pp.915-923
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• 1995

The parameters for an empirical net atomic charge calculation method, Modified Partial Equalization of Orbital Electronegativity (MPEOE), were determined for the atoms in organosilicon compounds and zeolites. For the organosilicon family, the empirical parameters were determined by introducing both experimental and ab initio observables as constraints, these are the experimental and ab initio dipole moments, and the ab initio electrostatic potential of the organosilicon molecules. The Mulliken population was also introduced though it is not a quantum mechanical observable. For the parameter optimization of the atoms in the aluminosilicates, the dipole moments and the electrostatic potentials which calculated from the 6-31G** ab initio wave function were used as constraints. The empirically calculated atomic charges of the organosilicons could reproduce both the experimental and the ab inito dipole moments well. The empirical atomic charges of the aluminosilicates could reproduce the ab initio electrostatic potentials well also.

• Bulletin of the Korean Chemical Society
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• v.22 no.9
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• pp.1005-1008
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• 2001

The lanthanide complexes have been anticipated to exhibit high efficiency along with a narrow emission spectrum. Photoluminescence for the lanthanide complex is characterized by a high efficiency since both singlet and triplet excitons are involve d in the luminescence process. However, the maximum external electroluminescence quantum efficiencies have exhibited values around 1% due to triplet-triplet annihilation at high current. Here, we proposed a new energy transfer mechanism to overcome triplet-triplet annihilation by the Eu complex doped into phosphorescent materials with triplet levels that were higher than singlet levels of the Eu complex. In order to show the feasibility of the proposed energy transfer mechanism and to obtain the optimal ligands and host material, we have calculated the effect depending on ligands as a factor that controls emission intensity in lanthanide complexes. The calculation shows that triplet state as well as singlet state of anion ligand affects on absorption efficiency indirectly.

• Bulletin of the Korean Chemical Society
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• v.12 no.4
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• pp.387-392
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• 1991

We present a theoretical investigation of the inelastic atom-surface phonon scattering for a model He-Si(100) system by the classical trajectory-quantum forced oscillator(DECENT) method. Single and multi-phonon transition probabilities of normal modes are calculated for several initial beam orientations and several initial kinetic energies. In order to understand surface structure effects, the calculation has been done on both reconstructed and unreconstructed surfaces of the He/Si(100) system. The origin of mode specificity for energy transfer is discussed. The contribution of one, two, and multi-phonon events to the total energy transfer between 0 and 600 K is also given.

• Bulletin of the Korean Chemical Society
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• v.21 no.5
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• pp.465-470
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• 2000

The conformations and energies of p-tert-butylcalix[4] crown-6-ether (1) and its alkyl ammonium complexes have been simulated by AM1 semi-empirical quantum mechanics and molecular mechanics calculations using a variety of forcefields (MM2, MM+, CVFF). We performed molecular dynamics calculations to simulate the behavior of these coplexes primartily focusing on the three representative conformations (cone, partial cone, 1,3-alternate) of host molecule 1. When we performed AM1 semi-empirical and molecular mechanics calculations, the one conformation was generally found to be most stable for all the employed calculation methods. The primary binding site of host 1 for the recognition of alkyl ammonium guests was confirmed to be the central part of the crown moiety. The complexation enthalpy calculations revealed that the alkyl amonium cations having smaller and linear alkyl group showed the better complexation efficiencies when combined with p-tert-butylcalix[4]crown-6-ether, that is in satisfactory agreement with the experimental results.

• Bulletin of the Korean Chemical Society
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• v.15 no.5
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• pp.357-360
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• 1994

The adsorption of cyanide ion on the gold electrode has been investigated by the subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS). The observations made by SNIFTIRS were consistent with those obtained by the polarization modulated Fourier transform infrared spectroscopy. According to the surface selection rule, cyanide ion appeared to adsorb on gold via either carbon or nitrogen lone pair electrons assuming a perpendicular orientation with respect to the metal surface. The possibility of presence of bridge-bound species seemed very infeasible. From the ab initio quantum mechanical calculation, adsorbate-to-metal bonding appeared to occur mainly via the $5{\sigma}$ donation from carbon to Au.