Abstract: Atomistic simulation calculations were performed to predict defect energies of vacancy clusters and dissociation energies of clusters with helium The computation technique was based on pair potentials and the Mott–Littleton methodology was used as implemented in the CASCADE code Both the full charge and the partial charge model were employed The partial charge model shows better agreement with experimental data reported in the literature The energetically most favourable spatial configurations for clusters composed of up to eight vacancies were determined and the associated formation energies calculated The results indicate that the three-dimensional growth of vacancy clusters in MgO is energetically favourable Next, the activation energies for dissociation of helium atoms from these vacancy clusters were calculated The activation energy for dissociation of a helium atom from vacancy clusters larger than a monovacancy is approximately 36 eV for the partial charge model Remarkably, the activation energy for dissociation of a helium atom from a monovacancy was found to be higher, 39 eV for the partial charge model This last energy is enhanced by lattice relaxation around the monovacancy The dissociation energies from large vacancy clusters is in good agreement with the permeation energy of 33 ± 03 eV obtained experimentally with a permeation experiment in which helium release was monitored with neutron depth profiling (NDP)

Abstract: New asymmetric biaryls have been synthesized in order to clarify the conditions necessary for charge-transfer transitions in photoexcited neutral compounds and biradical formation in doubly charged ground-state species. A parallel behavior for both types of approaches is observed and explained with a simple coupling model allowing prediction of the intermoiety coupling strength. It is shown that for weakly coupled biaryls the monoions are connected with charge localization and the dications and dianions form thermally excited biradicals while the fluorescence data indicate biradicaloid excited states connected with partial charge separation. More strongly coupled biaryls, on the other hand, result in diamagnetic species for the doubly charged ground-state ions, and a charge-transfer contribution in the fluorescence spectra of the neutral compound is absent.

Abstract: We have derived phase space and diffusion theories for a new hopping model of charge transport in polypeptides and thence for distal chemical kinetics. The charge is transferred between two carbamide groups on each side of the Cα atom hinging two amino acid groups. When the torsional angles on the hinge approach a certain region of the Ramachandran plot, the charge transfer has zero barrier height and makes charge transfer the result of strong electronic correlation. The mean first passage time calculated from this analytic model of some 164 fs is in reasonable agreement with prior molecular dynamics calculation of some 140 fs and supports this new bifunctional model for charge transport and chemical reactions in polypeptides.

Abstract: The Ge-Li bond in 1 reacts readily with water and oxygen to give 2 (Li/H exchange) and 3 (insertion), respectively. In both cases the partial charge and the oxidation state of the germanium atom changes. All compounds were characterized by X-ray crystallography.

Abstract: The 29Si NMR chemical shifts for a series of organically modified silane compounds, MexSi(OR)y(OH)4 − x − y (OR = OMe, OEt), were evaluated using a partial charge model (PCM) approach to describe the chemical bonding. These PCM results allow the relative contributions of the diamagnetic and paramagnetic terms in the 29Si NMR chemical shielding constant to be discussed. An explanation for the unique variations in the 29Si chemical shifts during for hydrolyzed organically modified silanes is presented.

Abstract: This work examines two partial oxidation reactions over oxides (alcohols dehydrogenation to aldehydes and aldehydes esterification to esters) to determine how reaction rates can be quantitatively correlated with physical properties of the bulk catalysts. We show that while electronegativity difference, Δχ, metal–oxygen bond strength, E M-O fail utterly, oxygen partial charge, qO, and oxygen Madelung potential, VMad (O), do provide limited correlations for the set of roughly twelve oxides examined. However, oxygen electronic polarisability, αO, does a much better job. We rationalise this finding in terms of the concept of chemical hardness in what appears to be the first successful application of this idea to oxide reactivity.

Abstract: Ab initio quantum mechanical calculations at the 6-31+G* basis set are reported on over 75 substituted ethanes and higher alkanes. The charges on the carbon and hydrogen atoms of these species are determined by topological- and orbital-based methods. The relative change in charge is used to determine how a substituent group affects atoms remote from it. Arguments are presented to account for the charge on the hydrogen atoms in substituted ethanes and higher alkanes. Fluorine atoms within about 2.7 A of hydrogen atoms cause an increase in positive charge on those hydrogen atoms. Charge is moved to the periphery of the molecule when a charged substituent is present. A model that involves through-space interactions between the charged group and the alkane framework accounts for these data. The charge calculations indicate a substituted carbon atom has a charge that is more dependent on the nature of the atom to which it is attached than on that atom's charge or on other atoms in the substituent. No evidence ...

Abstract: In order to study from a theoretical point of view the coordinative properties and explain the reported N5,O4-chelating behaviour in several oxopteridine derivatives, semiempirical molecular orbital calculations were carried out on lumazine (pteridine-2,4(1H,3H)-dione), its N- and C-methylated derivatives, as well as their deprotonated and protonated forms using the PM3 hamiltonian as implemented in the hyperchem 4.0 package. The study of the partial charges over donor atoms does not allow us to justify the reported N5,O4-coordinating scheme, because some positive charge has been found on the N5 atom. Therefore, a more detailed analysis has been carried out taking into account the contributions of the AOs of each atom to the LCAO that defines each frontier MO. These calculations have confirmed the N5-O4 coordination mode of the neutral lumazine derivatives. The anionic forms could act as ligands in several ways, including the formation of either four- (N1-N8, N3-O4, N3-O2) or five-membered chelate rings (N5,O4). The experimental occurrence of only the latter coordination mode must be related to the higher stability of the five-membered chelate rings if it is compared with those of four and the possibility to establish π-M–N5 back-bonding.

Abstract: Ab initio calculations have been performed in order to investigate a recently proposed polarizable model [M. C. C. Ribeiro, Phys. Rev. B 61, 3297 (2000)] for molecular dynamics (MD) simulation of the molten salt Ca0.4K0.6(NO3)1.4. On the basis of the electronegativity equalization method, polarization effects in the MD simulations have been introduced by a fluctuating charge (FC) model for the nitrate ion. Partial charges in the nitrate ion are obtained by ab initio calculations at several levels of theory, and compared with previously proposed models for MD simulations of nitrate melts. Charge fluctuation is achieved in the ab initio calculations by using positive probe charges placed around a nitrate ion. The parameters of the FC model are corroborated by comparison of the ab initio partial charges with the ones obtained directly by the electronegativity equalization method. Simulated annealing of a cluster including two double-charged cations and two nitrate ions shows that very different structures ar...

Abstract: The application of the well-known DLVO pair potential and its variations in the literature to the evaluation of the charge on macroions routinely results in an “effective” charge considerably smaller than the “bare” surface charge. Various theories have been proposed for “charge renormalization” on the basis of either surface effects (viz., counterion “condensation”) or equivalence of linearized and nonlinearized electrostatic potentials at the surface of a computation cell in the numerical analysis of the Poisson−Boltzmann equation. In the present discourse, a model for the effective charge is proposed that is based on the equivalence of the screened Coulomb macroion−counterion interaction to the thermal energy kBT. The distance at which these interactions are equal, Rtherm, defines a distance partition for the counterions into two populations: those tightly associated with the macroion and contributing to the charge reduction and those “free” in solution and contributing to the properties of the surrou...

Abstract: A metal cation–π (Na+-tryptophane) interaction was detected in the crystallographic structure of a thermophilic Bacillus stearothermophilus triosephosphate isomerase mutant (bTIMmut). The geometry of this particular interaction between a cation and an aromatic ring was analyzed, and theoretical descriptors were derived. In particular, the program GRID emerges as a rapid diagnostic tool to detect cation–π binding sites in (macro)molecules when an appropriate probe is used. This procedure offers an attractive alternative to ab initio calculated molecular electrostatic potential maps. The influence of different force fields (amber, cvff, cff91) and of a series of parameters [partial charge (q), dielectric constant (e), polarizability (via the Aij term of the nonbond Lennard–Jones potential)] was also tested in optimization procedures. The geometries of the complexes were compared to ab initio (molecular orbital—HF/6-31G**, and density functional theory—DFT[B3LYP]/6-31G**) calculations and experimental geometries of cation–π interactions observed in small molecules crystal structures. This work leads to an optimum methodology that was applied with success to the simulation of the cation–π interaction observed in bTIMmut. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 847–855, 2000

Abstract: The paper presents a variational method to distribute the charge transferred (CT) between an ion and a dielectric continuum onto a boundary element (BE) grid used to represent the dielectric continuum media. The CT charge is transferred into the dielectric using a methodology that combines a semiempirical effective Hamiltonian with a modified Poisson-Boltzmann equation, which includes CT in the form of a surface charge density positioned at the dielectric interface. The variational method eliminates the bias of the earlier method used to distribute CT charge into the dielectric, i.e., the need to specify the solute atoms used in constructing the BE grid. The surface pattern of the magnitudes of the CT charges placed onto the BE grid is obtained by minimizing an energy functional defined as the sum of the CT charge self-interaction energy and the energies due to CT charge interaction with the reaction field (RF) and solute partial atomic charges. The total energies due to CT charge interaction with the reaction field (RF) and solute partial atomic charges. The total amount of charge, distributed on the BE grid, is constrained to the amount of charge transferred from/to the solute HOMO-LUMO molecular orbital, by using the method of Lagrangemore » multipliers.« less

Abstract: This paper presents a theoretical model for the investigation of charge transfer between ions and a solvent treated as a dielectric continuum media. The method is a combination of a semiempirical effective Hamiltonian with a modified Poisson-Boltzmann equation which includes charge transfer in the form of a surface charge density positioned at the dielectric interface. The new Poisson-Boltzmann equation together with new boundary conditions results in a new set of equations for the electrostatic potential (or polarization charge densities). Charge transfer adds a new free energy component to the solvation free energy term, which accounts for all interactions between the transferred charge at the dielectric interface, the solute wave function and the solvent polarization charges. Practical calculations on a set of 19 anions and 17 cations demonstrate that charge exchange with a dielectric is present and it is in the range of 0.06-0.4 eu. Furthermore, the pattern of the magnitudes of charge transfer can be related to the acid-base properties of the ions in many cases, but exceptions are also found. Finally, we show that the method leads to an energy decomposition scheme of the total electrostatic energy, which can be used in mechanistic studies on protein and DNA interactionmore » with water. (c) 2000 American Institute of Physics.« less

Abstract: A polarizable model potential (PMP) function for methanol and three ions (Cl-, Na+, and Mg2+) is developed on the basis of high-level ab initio molecular orbital calculations (MP2/6-311++G(2d,2p)). The PMP function consists of Coulomb, polarization, and Lennard-Jones terms. The permanent partial charge parameters of the Coulomb term, and the multicenter polarizability parameters of the polarization term, are determined by using electrostatic potential optimization, and polarizable one-electron potential (POP) optimization, respectively. The Lennard-Jones parameters are adjusted to reproduce the ab initio potential energy surfaces of methanol dimer and ion−methanol complexes. The PMP function using the final parameters reproduced well the ab initio energy surfaces of methanol dimer, ion−methanol, and methanol−ion−methanol systems. The root-mean-square (rms) deviations of ion−methanol systems having various conformations are only 10−12% of the ab initio interaction energies. The electron density changes by ...

Abstract: Two kinds of 3,3′,5,5′-tetranitro-4,4′-biphenyldiol dianion (TNBP2−) molecules having different dihedral angles (φ) between the two phenyl rings exist in the tetrabutylammonium salt of TNBP2− (φ = 0° and 35°), while only one kind of TNBP2− molecule exists in the tetraphenylphosphonium salt (φ = 0°). The 4∶1 cation radical salt of BEDT-TTF (ET) with TNBP2− asa counter anion is metallic down to 3 K. The ET molecules form a two-dimensional conducting layer which is sandwiched by the layers of flat TNBP2− molecules (φ = 0°). The crystal structure indicates the β″432-type stacking of tetramerized ET molecules which is caused by hydrogen bonds between the CH groups of ET and the oxygen atoms (nitro and phenol) of TNBP2−. The optical spectra in a KBr pellet are consistent with both the highly conductive and distorted structural nature. The magnetic susceptibility at room temperature is high (χ = 6.7 × 10−4 emu spin−1) compared with the conventional organic metal based on ET (χ = 3.4–5.5 × 10−4 emu spin−1) indicating strong electron correlation in the 4∶1 complex. The temperature dependence of the magnetic susceptibility suggests a semimetallic nature which is consistent with the calculated Fermi surface. The calculated band width is comparable to the estimated effective on-site Coulomb repulsive energy. A semiconductive behavior with high conductivity is observed in the nearly 2∶1 ET complex of TNBP2−. A partial charge transfer state of the ET molecules is supported by the optical spectra. The high conductivity and optical data suggest that the 2∶1 salt is not (ET1+)2(TNBP2−) but most plausibly (ET0.5+)2(HTNBP1−).

Abstract: Two quasi-multipole electrostatic models for molecular charge distributions are presented. They assign arrays of point charges to nonhydrogen atoms on the basis of hybrid orbitals or localised molecular orbitals. When used with common semiempirical MO-techniques, they reproduce natural atomic orbital derived point charge (NAO-PC) and ab initio molecular potentials well. The localised orbital technique (LMO-PC) is intuitively more attractive than the hybrid orbital-point charge (HO-PC) method, although the former is more CPU-intensive.

Abstract: PROBLEM TO BE SOLVED: To evaluate integrity of inter-coil turns between insulation layers high sensitivity in a dynamo-electric machine, such as an electric motor having a winding comprising a plurality of turns of coil. SOLUTION: In the dynamo-electric machine, having a winding comprising a plurality of turns of coils, it is arranged so to include a power source unit (an inverter driver 11) for generating a surge voltage 4, a partial charge detection means 2 (through-type high-frequency current transformer 12) for detecting partial charge in an inter-turn insulation layers and a measurement judging means 3 for evaluating the value of the detected partial discharge. The surge voltage is applied to a circuit line side terminal of the winding, to generate a partial charge in the inter-turn insulation layer by a high voltage produced between the turns of coil near the circuit line side of the winding and the relation is measured between the value of the detected partial charge, the magnitude of the surge voltage and the steepness of the rising part thereof. Thus, the partial charge in the inter-turn insulation layer is judged being distinguished from the partial charge in the insulation layer to the ground of the coil from the relation obtained.

Abstract: Within a single-band Hubbard model, treated by means of a strong-coupling approach based on a cumulant expansion, we investigate the existence of critical charge fluctuations (CCF) that could give rise to a phase separation (PS) or a charge density wave, by means of a Bethe-Salpeter equation for the vertex function in the particle-hole channel. We discuss the relevance of the precursor effects of charge ordering on the self-energy of the electrons and the non-Fermi liquid behavior arising from an effective electron-electron interaction.

Abstract: We study the charge dynamics of α′-NaV 2 O 5 , a coupled anisotropic ladder system at quarter filling, by using an exact-diagonalization technique on small clusters of the trellis-lattice t – J – V model. We derive values of model parameters, and calculate the optical conductivity and dynamical density correlation function, to show that the charge ordering is caused by the observed anomalous fluctuations of the valence state of V ions. Effects of Na-deficiency are also discussed.

Abstract: Based on first-principles calculations, structure optimization of Pd intercalated graphite is performed and the equilibrium values for lattice constants are obtained, in agreement with experimental values. In graphite the carbon atoms within the basal plane are bound together by strong covalent σ-bonds, while atoms in adjacent layers are weakly bound by Van der Waals bonds, results in semimetal. Being intercalated with Pd, due to Pd-4d and C-2p hybridizations, partial charge transfers occur from Pd to C, which increase the density of states at Fermi level and make the compound metallic-like; the heat of formation is found to be 2.45eV for per Pd atom intercalation.

Abstract: Intrinsic charge transfer in mixed halide compounds Pt X\-xX′ 1-x was studied in the framework of the two\|band extended Pielerls\|Hubbard model. It was found that the number of transferred charges can be a fraction times of the electronic charge. The maximum amount of transferred charges occurs at a certain x for a given mixed compound.

Abstract: Effect of static charges on transport properties of disordered organic materials is considered. Long range nature of Coulomb interaction requires to take into consideration a finite thickness of the transport layer. Presence of conducting electrodes significantly modifies properties of organic medium, removes a long range Coulomb divergence,and makes it possible to calculate in finite form statistical properties of organic medium (with nonzero total charge density) , relevant for transport characteristics. A special attention is paid to the particular case of charge induceddisorder - a disorder originated from the surface charge located at the rough surface of electrodes. We present also ageneralization of 1D model of charge carrier transport to the case of inhomogeneous energetic disorder that realizesin the case of charge induced disorder.Keywords: Charge carrier transport, finite charge density, size effects 1. INTRODUCTION The essence of a modern paradigm of the charge carrier transport in disordered organic materials is a close connectionbetween spatial correlation of energy levels U() in particular material and its transport properties.1'2 The mostlywell understood reason for a strong spatial correlation is a presence in the transport material some particular kindof molecules, e.g. dipolar or quadrupolar molecules.13 The most important parameter of the theory is the variancea2