Showing papers by "Kwang S. Kim published in 2003"
TL;DR: The structures of pure gold and silver clusters (Auk, Agk, k = 1−13) and neutral and anionic gold−silver binary clusters (aumAgn, 2 ≤ k = m + n ≤ 7) have been investigated by using density functional theory (DFT) with generalized gradient approximation (GGA) and high level ab initio calculations.
Abstract: The structures of pure gold and silver clusters (Auk, Agk, k = 1−13) and neutral and anionic gold−silver binary clusters (AumAgn, 2 ≤ k = m + n ≤ 7) have been investigated by using density functional theory (DFT) with generalized gradient approximation (GGA) and high level ab initio calculations including coupled cluster theory with relativistic ab initio pseudopotentials. Pure Auk clusters favor 2-D planar configurations, while pure Agk clusters favor 3-D structures. In the case of Au, the valence orbital energies of 5d are close to that of 6s. This allows the hybridization of 6s and 5d orbitals in favor of planar structures of Auk clusters. Even 1-D linear structures show reasonable stability as local minima (or as global minima in a few small anionic clusters). This explains the ductility of gold. On the other hand, the Ag-4d orbital has a much lower energy than the 5s. This prevents hybridization, and so the coordination number (Nc) of Ag in Agk tends to be large in s-like spherical 3-D coordination i...
278 citations
TL;DR: In this article, the authors examined the nature of the cation−π interaction by carrying out high level ab initio calculations of both metallic (Li+,Na+,K+, and Ag+) and organic (NH4+, C(NH2)3+, and N(CH3)4+) cations with different classes of π systems, viz alkenes (ethene), arenes (benzene), and heteroarenes (pyrrole).
Abstract: The nature of the cation−π interaction has been examined by carrying out high level ab initio calculations of both metallic (Li+,Na+,K+, and Ag+) and organic (NH4+, C(NH2)3+, and N(CH3)4+) cations with different classes of π systems, viz. alkenes (ethene), arenes (benzene), and heteroarenes (pyrrole). The calculations, which include a rigorous decomposition of the interaction energies, indicate that the interaction of these π systems with the metal cations is characterized by contributions from both electrostatic and induction energies, with the contribution of the latter being dominant. Though the contributions of dispersion energies are negligible in the cation−π complexes involving Li+ and Na+, they assume significant proportions in the complexes involving K+ and Ag+. In the π complexes of the organic cations, the repulsive exchange contributions are much larger than the attractive electrostatic contributions in the π complexes of organic cations, and thus, the contributions of both induction and dispe...
222 citations
TL;DR: As unique tweezer-like binding of 1 with anions is predicted by the ab initio calculations, strong anion-binding properties of chemosensor 1 are demonstrated by using fluorescence as well as (1)H NMR.
164 citations
TL;DR: The association constant and free energy gain of the N-butyl receptor 2 for F(-) in acetonitrile were measured to be 2.1 x 10(5) M(-1) and -7.25 kcal/mol, respectively, showing that the receptor has a high affinity for F (F(-)) in highly polar organic solvents.
Abstract: A benzene-based tripodal imidazolium receptor utilizing the strong (C−H)+···X- hydrogen bonding interaction between imidazolium moieties and halide anions is extensively investigated both theoretically and experimentally. Ab initio calculations predict that this receptor has a very high affinity for fluoride ion (F-). The association constant and free energy gain of the N-butyl receptor 2 for F- in acetonitrile were measured to be 2.1 × 105 M-1 and −7.25 kcal/mol, respectively, showing that the receptor has a high affinity for F- in highly polar organic solvents.
139 citations
TL;DR: In this article, the authors investigated several new low-lying energy conformers in addition to previously reported ones and found the lowest energy conformer for the pentamer is found to have a wedge-like structure.
Abstract: Although various low-lying energy structures of electron–water clusters, e−–(H2O)2–6, have been reported, some of the global minimum energy structures (in particular, for the tetramer and pentamer) are still not clearly characterized yet Therefore, using high-level ab initio calculations, we have investigated several new low-lying energy conformers in addition to previously reported ones The lowest energy conformer for the pentamer is found to have a wedge-like structure which has never been studied before Based on the experimental vertical electron-detachment energies and OH vibrational spectra of the electron–water clusters, we report the most probable structures and their nearly isoenergetic structures The OH vibrational frequencies of e−(H2O)2–6 and e−HOD(D2O)1–5 are investigated, and are found to be in excellent agreement with the available experimental data Their O–H stretch frequency shifts are classified in terms of the types of water molecules
99 citations
TL;DR: In this article, the substitutional Co ions incorporated into polycrystalline Co-doped ferromagnetic rutile tend to cluster, and then the neighboring interstitial sites become energetically favorable for Co to reside.
Abstract: The local environment around magnetic impurity atoms was reported to be unchanged in a structural phase transition of nanocrystalline Co-doped ferromagnetic ${\mathrm{TiO}}_{2}.$ Our ab initio density functional theory investigations show that the substitutional Co ions incorporated into ${\mathrm{TiO}}_{2}$ rutile tend to cluster, and then the neighboring interstitial sites become energetically favorable for Co to reside. This suggests that a Co-doped rutile containing only substitutional Co may not be an appropriate reference bulk system in determining the local environment of Co in polycrystalline $(\mathrm{T}\mathrm{i},\mathrm{C}\mathrm{o}){\mathrm{O}}_{2}$ rutile. We also find that the interstitial Co is in the low spin state and destroys the spin polarization of the surrounding substitutional Co, and hence reduces the average magnetic moment of impurity atoms.
68 citations
TL;DR: In this paper, the authors investigated the changes in the electronic structure of Cu, Ag, and Au in going from three-dimensional (3D) to two-dimensional to one-dimensional structure.
Abstract: We investigated the changes in the electronic structure of Cu, Ag, and Au in going from three-dimensional (3D) to two-dimensional to one-dimensional structure. Compared to 3D case, the interatomic distance (cohesive energy per bond) shows significant drop (rise) as dimensionality decreases. The shallow $d$ bands of 3D become sharper and shallower, and for Cu (Au) reach just below (above) the Fermi level. This picture is very sensitive to the accuracy of the calculations and may affect the calculated properties of nanowires. The spin-orbit interaction is found to play a significant role in Au, altering the electronic structure considerably and increasing the number of conducting channels in 1D Au.
64 citations
TL;DR: In this paper, a simple one-step ring opening reaction mechanism was proposed, where the closed form in the excited state reached the open form through nonadiabatic curve crossing, and the reaction rate was determined to be in the range (1.7-4) x 10 1 0 s - 1.
Abstract: Photochromic ring opening reaction dynamics of 1,2-bis(2-methylbenzo[b]thiophen-3-yl)hexafluorocyclopentene in solution has been studied by femtosecond time-resolved fluorescence and transient absorption measurements. Time profiles of the transient absorption at several different probe wavelengths are identical, showing two time constants, 4 and 22 ps. The spontaneous fluorescence reveals time profiles identical to that in the transient absorption. A simple one step ring opening reaction mechanism is proposed, where the closed form in the excited state reaches the open form in the ground state through nonadiabatic curve crossing. The ring opening reaction rate is determined to be in the range (1.7-4) x 10 1 0 s - 1 . A single 66 cm - 1 wave packet motion in the excited state is observed, whose role on the ring opening reaction is speculated upon.
62 citations
TL;DR: In this article, the coordination number (Nc) of Ag+(H2O)n is predicted to be 2 for n = 2-6 at the density functional theory level, while the Nc for n=3-5 is 3, and that for n-6 is 4 at the second-order Moller-Plesset perturbation level.
Abstract: Owing to the utility of redox phenomena of silver in many chemical systems, it is important to understand the coordination chemistry of Ag+ ion and hence the hydration structure. The lowest-energy conformations of Ag+(H2O)1–6 are sensitive to the calculation method employed. The coordination number (Nc) of Ag+(H2O)n is predicted to be 2 for n=2–6 at the density functional theory level, while the Nc for n=3–5 is 3, and that for n=6 is 4 at the second-order Moller–Plesset perturbation level. Further accurate analysis based on coupled-cluster singles and doubles theory with perturbative corrections for triple excitations agrees with the MP2 results except that Nc of 4 is also as competitive as Nc of 3 for n=5. To identify the correct Nc, it would be useful to facilitate the IR experimental characterization. We thus provide the OH spectra for various possible structures. It is interesting to note that the hydration chemistry of Ag+ ion is somewhat different from that of alkali metal ions.
55 citations
TL;DR: In this paper, the authors investigated the solvent rearrangement process for the excited electron in the iodide-water hexamer using ab initio calculations and elucidated the transformation pathway from the low-lying energy structures of the ionized water hexamer to those of the electron-hexamer.
Abstract: The study of electron solvation dynamics is vital for understanding the phenomena related to the electron transfer process in solvents. On the basis of a recent femtosecond dynamics study of charge-transfer-to-solvent states in photoexcited iodide–water clusters [Lehr et al., Science 284, 635 (1999)], we have investigated the solvent rearrangement process for the excited electron in the iodide–water hexamer using ab initio calculations. Upon excitation of iodide–water hexamer, an electron transfers from the iodide anion to the water cluster. This results in release of the iodine atom and thereby formation of anionic water hexamer which undergoes rearrangement process toward the most stable conformation. The transformation pathway from the low-lying energy structures of the iodide–water hexamer to those of the electron–water hexamer is thus elucidated from the potential energy surface including the global and local minima and transition states of the electron–water hexamer.
51 citations
TL;DR: The structure of the electron-water heptamer has been investigated in this paper, and the lowest energy structure using ab initio calculations has been reported, and the relative energies, vertical electron-detachment energies, and OH vibrational frequencies of several lowest energy conformers are discussed.
Abstract: The electron–water heptamer is one of the “magic” numbers in the mass spectra of electron–water clusters, but up to now the structure of the electron–water heptamer is not known. Thus we have investigated a number of low-energy structures, and report the lowest-energy structure using ab initio calculations. The relative energies, vertical electron-detachment energies, and OH vibrational frequencies of several lowest energy conformers are discussed. As in the case of e−(H2O)6, the electron affinity for e−(H2O)7 is predicted to be positive, which would explain the intense peak observed in the time-of-flight mass spectra.
TL;DR: A novel receptor is designed, 1,3,5-tris(pyrrolyl)benzene, which shows high selectivity for acetylcholine (ACh), and the selectivity of the receptor for ACh over other ammonium cations is demonstrated by the ion-selective electrode (ISE) method in buffer solution.
TL;DR: In this paper, the authors investigated the equilibrium structures, binding energies, and vibrational frequencies of the water monomer/dimer complexes of p-benzoquinones and its corresponding negatively charged anionic species (Q− and Q2−).
Abstract: Since the energy conversion reactions in most biological systems involve the interactions of various negatively charged quinones with water molecules, we have investigated the equilibrium structures, binding energies, and vibrational frequencies of the water monomer/dimer complexes of p-benzoquinones (Q) and its corresponding negatively charged anionic species (Q− and Q2−). The calculations, which include the evaluation of charges and aromaticity, indicate the existence of double hydrogen bonds in the water monomer and water dimer complexes of neutral p-benzoquinone. When two water molecules are complexing with p-benzoquinone, a conformer exhibiting an H-bond between two water molecules (W2Q) is energetically more favored than the conformer WQW in which there is no direct interaction between the water molecules. However, an increase in the negative charge of p-benzoquinone leads to the energetic stabilization of the WQ2−W conformer over the Q2−W2 conformer. The charge transfer Q to water molecules is foun...
TL;DR: In this paper, the authors used ab initio density functional calculations to find that the monatomic AuZn and AuMg alloy wires have a truly linear structure as stable as the zig-zag one which is prone to form two-dimensional structures.
Abstract: Using ab initio density functional calculations, we find that the monatomic AuZn and AuMg alloy wires have a truly linear structure as stable as the zig--zag one which is prone to form two-dimensional structures. The energy barrier between these two phases is about 0.7 eV for AuZn wire and 0.5 eV for AuMg wire. The injection of s electrons into the gold wire by zinc or magnesium lifts the Fermi level and the resulting $s--p$ hybridization yields an energy minima for the linear structure, which is further stablized by the polarization effect arisen from the enhanced atomic charges.
TL;DR: In this article, the structure and electronic properties of ultrathin silver (Ag) nanowires self-synthesized in organic calix[4]hydroquinone (CHQ) nanotubes were investigated.
Abstract: We use first principles calculations to investigate the structure and electronic properties of ultrathin silver (Ag) nanowires self-synthesized in organic calix[4]hydroquinone (CHQ) nanotubes. The insulating CHQ nanotubes get transformed to semiconducting calix[4]diquinone-dihydroquinone (CQHQ) tubes in the presence of Ag. These encapsulated nanowires have linear crystalline structure. The electron density around the Fermi level is localized on the Ag nanowire. This indicates that the organic tubes act as shields between Ag nanowires, and the quantum confinement is possible in the encapsulated Ag nanowires like in quantum dots.
TL;DR: In this paper, the origin of dramatic variation in optical polarizabilities of push-pull conjugated chains with respect to the conjugation length is discussed, and the maximum ICT-driven coherence sizes of αCT and βCT are consistent with the time-dependent densities to the first and second orders of the electric field obtained from the collective electronic oscillators method.
Abstract: The origin of dramatic variation in optical polarizabilities of push–pull conjugated chains with respect to the conjugation length is discussed. Ab initio calculations of intramolecular charge transfer (ICT)-driven dipole moment (μCT), polarizability (αCT), and first hyperpolarizability (βCT) show that the values of αCT/μCT and βCT/μCT change linearly and quadratically with respect to the conjugation length, respectively. The maximum ICT-driven coherence sizes of αCT and βCT are consistent with the time-dependent densities to the first (ρ(1)) and second (ρ(2)) orders of the electric field obtained from the collective electronic oscillators method.
TL;DR: The use of femtosecond time-resolved degenerate four-wave mixing rotationally resolved spectroscopy to obtain very accurate structural information on the symmetric top cyclohexane is reported, highlighting the versatility of this method in determining accurate structures of large and complex molecules without dipole moment.
Abstract: In this paper, we report the use of femtosecond time-resolved degenerate four-wave mixing rotationally resolved spectroscopy to obtain very accurate structural information on the symmetric top cyclohexane. Apart from highlighting the versatility of this method in determining accurate structures of large and complex molecules without dipole moment, the present study also details the comparison of the experimentally determined rotational constant B0 with that obtained from high-level ab initio calculations. The theoretical calculations, which were carried out at both the second-order Moller−Plesset (MP2) and coupled-cluster with single, double, and perturbative triple substitutions [CCSD(T)] levels of theory, also take into account vibrational averaging effects. A detailed investigation of the vibrational averaging effects reveals that the corrections emerge from only the six highly symmetric A1g modes, a justification of which is provided by an analysis of these modes.
TL;DR: In this paper, the properties of various novel molecular systems including endo/exohedral fullerenes, nanotori, nonlinear optical materials, ionophores/receptors, polypeptides, enzymes, organic nanotubes, nanowires, and electronic and nano-mechanical molecular devices are investigated.
Abstract: Since theoretical investigations of gas phase clusters enable the evaluation of intrinsic molecular properties and intermolecular interactions, one can predict the macroscopic properties of bulk matter, from a microscopic determination of the properties of individual atoms, molecules, or clusters. Based on the insights obtained from theoretical investigations of the properties of a large number of cluster systems (ranging from simple water clusters to large π-systems), we have investigated the properties of various novel molecular systems including endo/exohedral fullerenes, nanotori, nonlinear optical materials, ionophores/receptors, polypeptides, enzymes, organic nanotubes, nanowires, and electronic and nano-mechanical molecular devices. The present minireview highlights some of the interesting results obtained in the course of our extensive theoretical investigations of clusters and nanomaterials.
TL;DR: In this paper, the curvature of charge distribution over the benzene clearly shows a good linear relationship with known experimental substituent constants, while the amount of charge transferred does not fully reflect the substitution effect.
Abstract: Charge distributions determining the electrostatic potential in monosubstituted benzenes are investigated. As a result, a new quantum chemical parameter for substituent effect, which would be useful in information coding (in terms of molecular electrostatic potential), is introduced. The curvature of charge distribution over the benzene clearly shows a good linear relationship with known experimental substituent constants, while the amount of charge transferred does not fully reflect the substituent effect. Because the curvature is a new and good quantum chemical parameter to describe the substituent effect, our results would be used as a strategy for design of new functional molecules such as molecular scale electronics using the electrostatic potential distributions.
TL;DR: In this article, the National Creative Research Initiative Center for Superfunctional Materials, Department of Chemistry, Division of Molecular and Life Sciences, Pohang University of Science and Technology, San 31, Hyojadong, Namgu, Poreng 790-784.
Abstract: National Creative Research Initiative Center for Superfunctional Materials, Department of Chemistry, Division of Molecular and Life Sciences, Pohang University of Science and Technology, San 31, Hyojadong, Namgu, Pohang 790-784, Korea Bioinformatics S/W Research Center, Department of Computer Sciences and Engineering, Pohang University of Science and Technology, San 31, Hyojadong, Namgu, Pohang 790-784, Korea Received June 28, 2003
TL;DR: Using ab initio and density functional calculations, the photoexcitation of a charge-balanced electron donor-acceptor (DA) complex comprised of tetracyanoethylene (TCE) and tetramethylethylene (TME) was studied in this paper.
Abstract: Using ab initio and density functional calculations, we studied photoexcitation of a charge-balanced electron donor–acceptor (DA) complex comprised of tetracyanoethylene (TCE) and tetramethylethylene (TME). We considered both the TCE-TME stacked conformer and a possible conformer with a solvent molecule (dichloromethane) inserted between TCE and TME. The photoexcitation of the DA complex can directly form a charge transfer (CT) state. Our theoretical investigations show that the CT state can also be produced from the decay of higher excited states. Using the continuum model, we investigated the solvent effects on CT absorption, local excitation, and CT emission in the polar solvent. The equilibrium solvation energies of the ground and excited states of the DA complex were calculated using the self-consistent reaction field method, and then the correction of nonequilibrium solvation energies for the vertical transitions was made. The transition energies (i.e., CT absorption for the DA complexes and CT emis...
TL;DR: The main emphasis is laid on the base-catalyzed epimerization reaction that drives the stereospecific recognition to near completion and the conducted tour mechanism is found to be the most likely candidate.
Abstract: The highly stereospecific and regiospecific recognition of α-amino acids exhibited by a novel Co(III) metal complex embodied in the experimental work (Nature 1999, 401, 254) is rationalized from the energetics and structural characteristics with the use of density functional calculations. The steric repulsion between the chiral center of the receptor [Co(III) complex] and alanine has been a cause for the discrimination of complex stabilities. The energies evaluated for all possible alanine binding modes clearly reveal regiospecificity. Our main emphasis is laid on the base-catalyzed epimerization reaction that drives the stereospecific recognition to near completion. The conducted tour mechanism is found to be the most likely candidate. A similar role by the equivalent Zn(II) complex is found.