Three-center expansion of electron repulsion integrals with linear combination of atomic electron distributions

A new systematic way of constructing auxiliary basis functions for approximating the evaluation of electron repulsion integrals is proposed and applied to SCF and MCSCF wavefunction calculations. In the approximation, the one-electron density is expanded in terms of a linear combination of atomic electron distributions (LCAD), and the four-center two-electron repulsion integrals are reduced to the three- and two-center quantities. This results in a high-accuracy approximation as well as a large reduction in disk storage and input/output requirement, proportional to N³ rather than N⁴, N being the number of basis functions. Numerical results indicate that the error from the present approximation decreases as the size of molecular basis functions increases and that the LCAD version of MCSCF calculations requires only a fractional amount of the CPU time required in the conventional procedure without loss of accuracy.     

Separation of two overlapping redox waves by cyclic-voltammo-thermometry: Applications to Cu/CuCl and Ag/AgCl systems in chloride solutions

When two reactions take place at a given potential, other information is necessary, in addition to the relation between the applied potential and electric current, in order to evaluate the individual contribution of the reactions. Information about the heat evolved at the electrode during cyclic voltammetry enables the reaction components to be separated. It is concluded that the Cu/Cu^I redox system in chloride solution (0.1 < [Cl^?] < 0.45 M) giving a simple CV curve, can be divided into two reactions: Cu/CuCl_ad and Cu/CuCl^?₂. A similar overlap of the Ag/AgCl_ad and Ag/AgCl^?₂ reactions is also observed for the Ag/Ag^I redox system in 7 < [Cl^?] < 9 M solutions.     

In vivo imaging of brain dopaminergic neurotransmission system in small animals with high-resolution single photon emission computed tomography.

High-resolution single photon emission computed tomography (SPECT) provides a unique capability to image the biodistribution of radiolabeled molecules in small laboratory animals. Thus, we applied the high-resolution SPECT to in vivo imaging of the brain dopaminergic neurotransmission system in common marmosets using two radiolabeled ligands, [123I]2beta-carbomethoxy-3beta-(4-iodophenyl)tropane (beta-CIT) as a dopamine transporter (DAT) ligand and [123I]iodobenzamide (IBZM) as a dopamine D2 receptor (D2R) ligand. Specific images of the striatum, a region with a high density of dopaminergic synapses, were obtained at 240 min and 60 min after injection of [123I]beta-CIT and [123I]IBZM, respectively. Furthermore, a significantly low accumulation of [123I]beta-CIT in the striatum was observed in MPTP-treated animals compared with results for a control group, and a similar accumulation in the control group was observed with the pretreatment of deprenyl in the MPTP-treated animals. However, the striatal accumulation of [123I]IBZM showed no changes among the control, MPTP-treated, and deprenyl-MPTP-treated groups. These SPECT imaging results agreed well with those of DA concentration and motor behavior. Since MPTP destroys nigrostriatal dopamine nerves and produces irreversible neurodegeneration associated with Parkinsonian syndrome, SPECT imaging data in this study demonstrated that deprenyl shows its neuroprotective effect on Parkinsonism by protecting against the destruction of presynaptic dopamine neurons.     

Proton dynamics in superionic phase of Tl3H(SO4)2

Electrical properties and ¹H-NMR absorption line have been measured, in order to investigate proton dynamics in a superionic phase in Tl₃H(SO₄)₂. From the measurement of the thermoelectric power, it is found that a majority carrier in electrical conductivity is a proton. Moreover, from ¹H-NMR measurement it is also found that the activation energy 0.33 eV of the hopping motion of protons is close to 0.38 eV as observed in the electrical conductivity measurement. These results indicate that the electrical conductivity in the superionic phase is caused by the hopping motion of protons accompanied by the breaking of the hydrogen bonds.     

Characterization of zinc-modified lithium tantalate thin films fabricated by chemical solution deposition method

Zinc-substituted lithium tantalate thin films were fabricated for improving the electrical resistivity by compensating the valence of lattice defects in LiTaO₃ crystal. The films with the chemical composition of (Li_1.00-x Zn _x )TaO₃ were fabricated on (111)Pt/TiO₂/SiO₂/(100)Si substrate by a chemical solution deposition technique using metal-organic precursors. Dense films consisting of a ilumenite-type crystalline phase were deposited by spin coating on the substrates, followed by heat-treatment at 650°C for 5 min in air. The leakage current density of the LiTaO₃ film was reduced from approximately 10⁻⁴ to 10⁻⁶ A/cm² by substituting Zn²⁺ ions for Li⁺ ions in the LiTaO₃ films. Polarization–electric field hysteresis loop was improved significantly by partial substitution of Zn²⁺ for Li⁺ ions, which is based on the enhancement of electrical resistivity.     

A new family of spin crossover complexes with a tripod ligand containing three imidazoles: synthesis, characterization, and magnetic properties of [FeIIH3LMe](NO3)2.1.5H2O, [FeIIILMe].3.5H2O, [FeIIH3LMe][FeIILMe]NO3, and [FeIIH3LMe][FeIIILMe](NO3)2 (H3LMe) = Tris[2-(((2-methylimidazol-4-yl)methylidene)amino)ethyl]amine)

A new family of spin crossover complexes, [Fe(II)H(3)L(Me)](NO(3))(2).1.5H(2)O (1), [Fe(III)L(Me)].3.5H(2)O (2), [Fe(II)H(3)L(Me)][Fe(II)L(Me)]NO(3) (3), and [Fe(II)H(3)L(Me)][Fe(III)L(Me)](NO(3))(2) (4), has been synthesized and characterized, where H(3)L(Me) denotes a hexadentate N(6) tripod ligand containing three imidazole groups, tris[2-(((2-methylimidazol-4-yl)methylidene)amino)ethyl]amine. It was found that the spin and oxidation states of the iron complexes with this tripod ligand are tuned by the degree of deprotonation of the imidazole groups and by the 2-methyl imidazole substituent. Magnetic susceptibility and M?ssbauer studies revealed that 1 is an HS-Fe(II) complex, 2 exhibits a spin equilibrium between HS and LS-Fe(III), 3 exhibits a two-step spin transition, where the component [Fe(II)L(Me)](-) with the deprotonated ligand participates in the spin transition process in the higher temperature range and the component [Fe(II)H(3)L(Me)](2+) with the neutral ligand participates in the spin transition process in the lower temperature range, and 4 exhibits spin transition of both the Fe(II) and Fe(III) sites. The crystal structure of 3 consists of homochiral extended 2D puckered sheets, in which the capped tripodlike components [Fe(II)H(3)L(Me)](2+) and [Fe(II)L(Me)](-) are alternately arrayed in an up-and-down mode and are linked by the imidazole-imidazolate hydrogen bonds. Furthermore, the adjacent 2D homochiral sheets are stacked in the crystal lattice yielding a conglomerate as confirmed by the enantiomeric circular dichorism spectra. Compounds 3 and 4 showed the LIESST (light induced excited spin state trapping) and reverse-LIESST effects upon irradiation with green and red light, respectively.     

Superposition of nonorthogonal Slater determinants towards electron correlation problems

We propose variational and nonvariational methods based on the superposition of nonorthogonal Slater determinants. Properties of the reference functions are discussed. In the nonorthogonal configuration interaction method, all the excited configurations of multiple determinants are integrated into a variational space. An efficient way to manipulate matrix elements over determinants of distinct vacuums is presented by introducing similarity transformed operator and bracket transformations. The method enables us to map a matrix multiplication in the nonorthogonal problem to an orthogonal one, and thus maintains a fundamental scaling property along with the amount of data processed in the corresponding orthogonal configuration interaction method. Furthermore, we discuss a coupled-cluster theory employing a vacuum-dependent wave operator, which is entirely size consistent as well as core extensive. These methods are applied to H₂O + nHe(n = 0−2) and a single-bond dissociation of the HF molecule, compared with conventional methods including full and multireference configuration interaction methods. Received: 7 July 1997 / Accepted: 12 September 1997     

Amperometric glucose-sensing electrode based on carbon paste containing poly (ethylene glycol)-modified glucose oxidase and cobalt octaethoxyphthalocyanine

An amperometric enzyme electrode for glucose was prepared by incorporating poly (ethylene glycol)-modified glucose oxidase and cobalt octaethoxyphthalocyanine [CoPc(OEt)₈], a new mediator, into a carbon paste matrix. The polymer-modified enzyme exhibited a higher activity than the native enzyme in the hydrophobic carbon paste medium. CoPc(OEt)₈ could oxidize the enzyme at more negative potentials than unsubstituted cobalt phthalocyanine (CoPc). Further, the CoPc(OEt)₈-mediated enzyme electrode showed a high stability: the electrode response to glucose did not decrease for at least 4 weeks (or for 700 assays), whereas the glucose response from a CoPc-mediated enzyme electrode fell to half of the initial value within 2 weeks (or after 300 assays). CoPc(OEt)₈, a paraffin-oil soluble derivative of CoPc, incorporated in the bulk of carbon paste, diffused towards the electrode surface so as to renew continuously the electrode surface, which resulted in the high stability of the new mediator-based enzyme electrode.     

Implementation of the CCSD(T)-F12 method using cusp conditions

The explicitly-correlated coupled-cluster singles and doubles with perturbative triples method (CCSD(T)-F12) is implemented using the cusp conditions. Numerical tests for a set of 16 molecules have shown agreement of correlation energies within 1 mE(h) between the cusp-condition and fully-optimized CCSD(T)-F12 methods. Benchmark calculations on 13 chemical reactions with the cusp-condition CCSD(T)-F12 method reproduce experimental enthalpies within 2 kJ mol(-1). It is also shown that regular unitary-invariant ansatz cannot exactly satisfy singlet and triplet cusp conditions in open-shell situations. We present an extended ansatz which can handle both conditions exactly.     

Comparative study on solvation free energy expressions in reference interaction site model integral equation theory

The performance of the recently proposed partial wave (PW) free energy functional is compared with those of two previous expressions, Gaussian fluctuation (GF) and hypernetted chain (HNC), within the reference interaction site model framework. The applications to the calculations of ambient and supercritical water, solvation free energies of organic molecules, and partition coefficients clearly show that the PW and GF free energy expressions provide more reliable results than the HNC functional, indicating rather associative situations of geometry in ordinary liquids of medium-sized molecules.