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Lee, Byung-Dae,Lee, Min-Joo Korean Chemical Society 2009 Bulletin of the Korean Chemical Society Vol.30 No.4
The predictions of the radical reaction sites for phenol, 2-, 3- and 4-chlorophenols (CPs) and 4-chloronitrobenzene (CNB) were studied by atomic charge distribution calculations. The atomic charge distributions on each atom of these molecules were obtained using the CHelpG and MK (Merz-Kollman/Singh) methods with the optimized structural parameters determined by DFT calculation at the level of BLYP/6-311++G(d,p). By comparing the experimentally obtained hydroxyl addition site(s) and the calculated atomic charges on carbon atoms of phenol and CPs, we found that hydroxyl substitution by oxidation reaction mainly occurred to the carbon(s) with high atomic charges. With these results, we were easily able to predict the position(s) of the ·OH reaction site(s) of phenol, CPs and CNB through atomic charge distribution calculations.
Dynamical Metal to Charge-Density-Wave Junctions in an Atomic Wire Array
Song, Sun Kyu,Samad, Abdus,Wippermann, Stefan,Yeom, Han Woong American Chemical Society 2019 NANO LETTERS Vol.19 No.8
<P>We investigated the atomic scale electronic phase separation emerging from a quasi-1D charge-density-wave (CDW) state of the In atomic wire array on a Si(111) surface. Spatial variations of the CDW gap and amplitude are quantified for various interfaces of metallic and insulating CDW domains by scanning tunneling microscopy and spectroscopy (STS). The strong anisotropy in the metal-insulator junctions is revealed with an order of magnitude difference in the interwire and intrawire junction lengths of 0.4 and 7 nm, respectively. The intrawire junction length is reduced dramatically by an atomic scale impurity, indicating the tunability of the metal-insulator junction in an atomic scale. Density functional theory calculations disclose the dynamical nature of the intrawire junction formation and tunability.</P> [FIG OMISSION]</BR>
Impurity-Mediated Early Condensation of a Charge Density Wave in an Atomic Wire Array
Yeom, Han Woong,Oh, Deok Mahn,Wippermann, Stefan,Schmidt, Wolf Gero American Chemical Society 2016 ACS NANO Vol.10 No.1
<P>We directly show how impurity atoms induce the condensation of a representative electronic phase, the charge density wave (CDW) phase, in atomic scale with scanning tunneling microscopy. Oxygen impurity atoms on the self-assembled metallic atomic wire array on a silicon crystal condense the CDW locally above the pristine transition temperature. More interestingly, the CDW along the wires is induced not by a single atomic impurity but by the cooperation of multiple impurities. First principles calculations disclose the mechanism of the cooperation as the coherent superposition of the local lattice strain induced by impurities, stressing the coupled electronic and lattice degrees of freedom for the CDW. This opens the possibility of the strain engineering over electronic phases of atomic-scale systems.</P>
Comparative Atomic Charges on Na+-(H2O)n (n = 1–6) Clusters
Nizam Uddin,최철호 대한화학회 2015 Bulletin of the Korean Chemical Society Vol.36 No.3
The performance of our mean gradient charge (MGC) concept was systematically investigated by adopting Na+-(H2O)n (n = 1–6) model clusters. The Mulliken charges are sensitive to the choice of theories and basis sets, and ChelpG charges abnormally behave with the system size. MGC and “atoms-in-molecules” (AIM) show small mean standard deviations (~0.02) with the choice of the theory and the basis set. However, an unpredictable value was found in AIM predictions. Both natural population analysis (NPA) and MGC yielded smooth and monotonic curves as a function of the system size. Therefore, MGC appears to have desirable properties in the consistent and reliable predictions of atomic charges.
Kim, Sang Woo,Wang, Yang,You, Hoseon,Lee, Wonho,Michinobu, Tsuyoshi,Kim, Bumjoon J. American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.39
<P>Substitution of C atoms in a polymer backbone by N atoms allows for the facile tuning of the energy levels as well as the backbone conformation and packing structures of conjugated polymers. Herein, we report a series of three polymer acceptors (<I>P</I><SUB>A</SUB>s) with N atoms introduced at different positions of the backbone and investigate how these N atoms affect the device performances of all-polymer solar cells (all-PSCs). The three <I>P</I><SUB>A</SUB>s, namely, P(NDI2DT-BTT), P(NDI2DT-PTT), and P(NDI2DT-BTTz), are composed of naphthalenediimide (NDI)-based and benzothiadiazole (BT)-based derivatives (dithiophene-BT (BTT), dithiophene-thiadiazolepyridine (PTT), and dithiazole-BT (BTTz)). The PTT and BTTz units are synthesized by replacing the C atoms in BT and thiophene, respectively, with N atoms, which effectively tune the optical, electrochemical, and charge-transporting properties of the corresponding <I>P</I><SUB>A</SUB>s. The all-PSCs using poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl))benzo[1,2-<I>b</I>:4,5-<I>b</I>′]dithiophene)-<I>co</I>-(1,3-di(5-thiophene-2-yl)-5,7-bis(2-ethylhexyl)benzo[1,2-<I>c</I>:4,5-<I>c</I>′]dithiophene-4,8-dione)] (PBDB-T) as a polymer donor and P(NDI2DT-PTT) as <I>P</I><SUB>A</SUB> exhibit a significantly enhanced power conversion efficiency (PCE) of 6.95%, whereas the all-PSCs based on the other <I>P</I><SUB>A</SUB>s show relatively lower PCEs (6.02% for PBDB-T:P(NDI2DT-BTT) and 1.43% for PBDB-T:P(NDI2DT-BTTz)). The high PCE of the PBDB-T:P(NDI2DT-PTT) device is due to the superior charge transfer and charge dissociation, resulting from the closely matched energy levels between PBDB-T and P(NDI2DT-PTT), as well as a more favorable bulk heterojunction morphology with improved miscibility. Importantly, the P(NDI2DT-PTT)-based all-PSC device shows improved air stability compared to the P(NDI2DT-BTT)-based device, which is most likely due to a decreased lowest unoccupied molecular orbital level of the <I>P</I><SUB>A</SUB>. Our findings suggest that the incorporation of N atoms into the <I>P</I><SUB>A</SUB>s is an effective strategy for improving the efficiency and stability of all-PSCs.</P> [FIG OMISSION]</BR>
A New Charge Analysis Derived From the Results of Semi-Emprical Mo-Lcao Calculation
Yilmaz, Hayriye,Ceyhan, Emre Cahit,Guzel, Yahya Korean Chemical Society 2012 대한화학회지 Vol.56 No.2
In this study we present a new approach for computing the partial atomic charge derived from the wavefunctions of molecules. This charge, which we call the "y_charge", was calculated by taking into account the energy level and orbital populations in each molecular orbital (MO). The charge calculations were performed in the software, which was developed by us, developed using the C# programming language. Partial atomic charges cannot be calculated directly from quantum mechanics. According to a partitioning function, the electron density of constituent molecular atoms depends on the electrostatic attraction field of the nucleus. Taking into account the Boltzmann population of each MO as a function of its energy and temperature we obtain a formula of partial charges.
Jae-Bok Seol,Young-Tae Kim,Bo-Hwa Kim,박찬경 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.1
The characterization of ZnO nanowires is crucial for developing nanostructured devices together with related compounds and alloys with an atomic-scale regime. This study describes the effects of laser energy on the atom probe tomography analysis of a single ZnO nanowire with a high aspect ratio, diameters of 80−100 nm and lengths of 10 μm. We observed both an asymmetrical evolution in the apex morphology and the compositional nonuniformities of Zn and O ions with respect to the laser energies ranging from 5 to 40 nJ. When the higher laser illumination exposed to the ZnO nanowires, non-uniform field strength becomes noticeable especially at the laser incident side of the samples. Moreover, we measured the charge state ratios of Zn + and Zn 2+ ions as a function of the applied laser energies. Our results proved important for accurate quantitative characterization and better interpretation for the laser-pulsed atom probe tomography of ZnO-based devices.
Magnetism in Single Metalloorganic Complexes Formed by Atom Manipulation
Choi, T.,Badal, M.,Loth, S.,Yoo, J.-W.,Lutz, C. P.,Heinrich, A. J.,Epstein, A. J.,Stroud, D. G.,Gupta, J. A. American Chemical Society 2014 NANO LETTERS Vol.14 No.3
<P>The magnetic properties of molecular structures can be tailored by chemical synthesis or bottom-up assembly at the atomic scale. We used scanning tunneling microscopy to study charge and spin transfer in individual complexes of transition metals with the charge acceptor, tetracyanoethylene (TCNE). The complexes were formed on a thin insulator, Cu<SUB>2</SUB>N on Cu(100), by manipulation of individual atoms and molecules. The Cu<SUB>2</SUB>N layer decouples the complexes from Cu electron density, enabling direct imaging of the TCNE molecular orbitals as well as spin-flip inelastic electron tunneling spectroscopy. Results were obtained at low temperature down to 1 K and in magnetic fields up to 7 T in order to resolve splitting of spin states in the complexes. We also performed spin-polarized density functional theory calculations to compare with the experimental data. Our results indicate that charge transfer to TCNE leads to a change in spin magnitude, Kondo resonance, and magnetic anisotropy for the metal atoms.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2014/nalefd.2014.14.issue-3/nl404054v/production/images/medium/nl-2013-04054v_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl404054v'>ACS Electronic Supporting Info</A></P>