Toyota Physical and Chemical Research Institute

Toyota, Japan

Toyota Physical and Chemical Research Institute

Toyota, Japan

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Watanabe S.,Kyushu Institute of Technology | Miyake K.,Toyota Physical and Chemical Research Institute
Journal of the Physical Society of Japan | Year: 2013

The mechanism of emergence of robust quantum criticality in Yb- and Ce-based heavy electron systems under pressure is analyzed theoretically. By constructing a minimal model for quasicrystal Yb15Al 34Au51 and its approximant, we show that quantum critical points of the first-order valence transition of Yb appear in the ground-state phase diagram with their critical regimes being overlapped to be unified, giving rise to a wide quantum critical regime. This well explains the robust unconventional criticality observed in Yb15Al34Au 51 under pressure. We also discuss broader applicability of this mechanism to other Yb- and Ce-based systems such as β-YbAlB4 showing unconventional quantum criticality. © 2013 The Physical Society of Japan.


Miyake K.,Toyota Physical and Chemical Research Institute | Watanabe S.,Kyushu Institute of Technology
Journal of the Physical Society of Japan | Year: 2014

Quantum criticality due to the valence transition in some Yb-based heavy fermion metals has gradually turned out to play a crucial role to understand the non-Fermi liquid properties that cannot be understood from the conventional quantum criticality theory due to magnetic transitions. Namely, critical exponents giving the temperature (T) dependence of the resistivity &rho(T), the Sommerfeld coef ficient, C(T)/T, the magnetic susceptibility, χ(T), and the NMR relaxation rates, 1/(T1T), can be understood as the effect of the critical valence fluctuations of f electrons in Yb ion in a unified way. There also exist a series of Ce-based heavy fermion metals that exhibit anomalies in physical quantities, enhancements of the residual resistivity ρ0 and the superconducting critical temperature (Tc) around the pressure where the valence of Ce sharply changes. Here we review the present status of these problems both from experimental and theoretical aspects. © 2014 The Physical Society of Japan.


Maeda S.,Hokkaido University | Ohno K.,Toyota Physical and Chemical Research Institute | Morokuma K.,Kyoto University | Morokuma K.,Emory University
Physical Chemistry Chemical Physics | Year: 2013

Global reaction route mapping (GRRM), a fully-automated search for all important reaction pathways relevant to a given purpose, on the basis of quantum chemical calculations enables systematic elucidation of complex chemical reaction mechanisms. However, GRRM had previously been limited to very simple systems. This is mainly because such calculations are highly demanding even in small systems when a brute-force sampling is considered. Hence, we have developed two independent but complementary methods: anharmonic downward distortion following (ADDF) and artificial force induced reaction (AFIR) methods. ADDF can follow reaction pathways starting from local minima on the potential energy surface (PES) toward transition structures (TSs) and dissociation channels. AFIR can find pathways starting from two or more reactants toward TSs for their associative reactions. In other words, ADDF searches for A → X type isomerization and A → X + Y type dissociation pathways, whereas AFIR finds A + B → X (+ Y) type associative pathways. Both follow special paths called the ADDF path and the AFIR path, and these tend to pass through near TSs of corresponding reaction pathways, giving approximate TSs. Such approximate TSs can easily be re-optimized to corresponding true TSs by standard geometry optimizations. On the basis of these two methods, we have proposed practical strategies of GRRM. The GRRM strategies have been applied to a variety of chemical systems ranging from thermal- and photochemical-reactions in small systems to organometallic- and enzyme-catalysis, on the basis of quantum chemical calculations. In this perspective, we present an overview of the GRRM strategies and some results of applications. Their practical usage for systematic prediction is also discussed. © the Owner Societies 2013.


The third order single excitation perturbation theory corrected with the dispersion energy based on the locally projected molecular orbital was applied to study the weak electron-donor-acceptor (charge-transfer) complexes and the hydrogen bonds in the water clusters. In the weak electron-donor-acceptor complexes, the dispersion energy is larger than the charge-transfer energy in absolute value. The dispersion energy is as large as the charge-transfer energy in the hydrogen bond. The cage form of (H 2O) 6 is the most stable among eight isomers examined, because the dispersion energy is the largest among them. © 2012 the Owner Societies.


Iwata S.,Toyota Physical and Chemical Research Institute
Journal of Physical Chemistry A | Year: 2010

The efficient code to evaluate the molecular interaction energy at the Hartree-Fock level of theory is developed. The method is the third-order single excitation perturbation theory based on the locally projected (LP) molecular orbitals (MO). It is shown that with a proper scaling of the molecular orbital integrals the basis set superposition error can be under controll even with a small size of basis sets. If the basis set contains augmented diffuse functions, the interaction energy, close to the counterpoise corrected energy, can be directly evaluated without the scaling, as fast as a single supermolecule Hartree-Fock calculation. The key of the method is to use the absolutely local occupied and excited MOs. With these MOs, the amount of the charge-transfer (CT) and the energy contribution of the CT terms are evaluated. © 2010 American Chemical Society.


Miyake K.,Toyota Physical and Chemical Research Institute
Journal of the Physical Society of Japan | Year: 2014

It is shown that an extra magnetization is induced by an onset of the equal-spin-pairing of spin triplet superconductivity if the energy dependence of the density of states of quasiparticles exists in the normal state. It turns out that the effect is observable in Sr2RuO4 due to the existence of van Hove singularity in the density of states near the Fermi level, explaining the extra contribution in the Knight shift reported by Ishida et al. It is also quite non-trivial that this effect exists even without external magnetic field, which implies that the time reversal symmetry is spontaneously broken in the spin space. ©2014 The Physical Society of Japan.


Nogami M.,Toyota Physical and Chemical Research Institute
Journal of Physical Chemistry B | Year: 2015

(Chemical Equation Presented) Superior functional glasses doped with rare-earth ions have been prepared by controlling the valence states of rare-earth ions. However, recent work has revealed unresolved questions about the controlling mechanism of rare-earth ions' valence states. To address these questions, oxide glasses with and without Al2O3 and doped with Eu3+ ions were prepared by a melting process; then, the valence states of Eu3+ ions were investigated during heating under a hydrogen environment. The Eu3+ ions were reduced to Eu2+ only in the glass containing Al3+ ions; the reduction occurred in the center of the glass over a short heating period. It was discovered that the reduction of Eu3+ ions concurrently occurred with the formation of OH bonds which were bound with Al3+ ions. Considering this and the data for the H2 gas diffusion through the glass, we conclude that diffusing H2 gas molecules react with Al-O- bonds surrounding Eu3+ ions to form AlOH bonds and reduce Eu3+ ions to Eu2+ via the extracted electrons. When H2 reacts with a glass structure, that hydrogen has transformed into - OH bonds and the hydrogen concentration in the glass decreases. In order to make up the lost hydrogen, more hydrogen molecules can enter into the glass, resulting in the fast reduction of Eu3+ ions in the center of the glass. © 2015 American Chemical Society.


Matsuura H.,University of Tokyo | Miyake K.,Toyota Physical and Chemical Research Institute
Journal of the Physical Society of Japan | Year: 2013

The effects of a spin-orbit interaction on transition-metal ions of (4d)3- and (5d)3-based oxides in which three electrons occupy t2g orbitals are studied. The amplitude of the magnetic moment of d electrons on the 5d and 4d orbitals is estimated by numerical diagonalization. It is found that the magnetic moment is reduced by the spin-orbit interaction. It is suggested that (4d)3- and (5d) 3-based oxides are located in the middle of the L-S and J-J coupling schemes. © 2013 The Physical Society of Japan.


Iwata S.,Toyota Physical and Chemical Research Institute
Journal of Chemical Physics | Year: 2011

The dispersion terms are evaluated with the perturbation theory based on the locally projected molecular orbitals. A series of model systems, including some of the S22 set, is examined, and the calculated binding energies are compared with the published results. The basis set dependence is also examined. The dispersion energy correction is evaluated by taking into account the double excitations only of the dispersion type electron configurations and is added to the 3rd order single excitation perturbation energy, which is a good approximation to the counterpoise (CP) corrected Hartree-Fock (HF) binding energy. The procedure is the approximate CP corrected HF D method. It ensures that the evaluated binding energy is approximately free of the basis set superposition error without the CP procedure. If the augmented basis functions are used, the evaluated binding energies for the predominantly dispersion-bound systems, such as rare gas dimers and halogen bonded clusters, agree with those of the reference calculations within 1 kcalmol-1 (4 kJmol -1). The limitation of the present method is also discussed. © 2011 American Institute of Physics.


Yakushi K.,Toyota Physical and Chemical Research Institute
Crystals | Year: 2012

This paper reviews charge ordering in the organic conductors, β″-(BEDT-TTF) (TCNQ), θ-(BEDT-TTF)2X, and α-(BEDT-TTF)2X. Here, BEDT-TTF and TCNQ represent bis(ethylenedithio)tetrathiafulvalene and 7,7,8,8-tetracyanoquinodimethane, respectively. These compounds, all of which have a quarter-filled band, were evaluated using infrared and Raman spectroscopy in addition to optical conductivity measurements. It was found that β″-(BEDT-TTF)(TCNQ) changes continuously from a uniform metal to a chargeordered metal with increasing temperature. Although charge disproportionation was clearly observed, long-range charge order is not realized. Among six θ-type salts, four compounds with a narrow band show the metal-insulator transition. However, they maintain a large amplitude of charge order (Δρ~0.6) in both metallic and insulating phases. In the X = CsZn(SCN)4 salt with intermediate bandwidth, the amplitude of charge order is very small (Δρ < 0.07) over the whole temperature range. However, fluctuation of charge order is indicated in the Raman spectrum and optical conductivity. No indication of the fluctuation of charge order is found in the wide band X = I3 salt. In α-(BEDT-TTF)2I3 the amplitude of charge order changes discontinuously from small amplitude at high temperature to large amplitude (Δρmax~0.6) at low temperature. The long-range chargeordered state shows ferroelectric polarization with fast optical response. The fluctuation of multiple stripes occurs in the high-temperature metallic phase. Among α-(BEDTTTF) 2MHg(SCN)4 (X = NH4, K, Rb, Tl), the fluctuation of charge order is indicated only in the X = NH4 salt. α′-(BEDT-TTF)2IBr2 shows successive phase transitions to the ferroelectric state keeping a large amplitude of charge order (Δρmax~0.8) over the whole temperature range. It was found that the amplitude and fluctuation of charge order in these compounds is enhanced as the kinetic energy (bandwidth) decreases. © 2011 by the authors; licensee MDPI, Basel, Switzerland.

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