Kazuo Tsumuraya - Academia.edu (original) (raw)

Papers by Kazuo Tsumuraya

The pseudogaps in compounds give a unique electronic character in the materials such as the ones ... more The pseudogaps in compounds give a unique electronic character in the materials such as the ones in the skutterudites. The Al3V compound with DO22 structure has also a deep pseudogap that has been explained by the presence of the covalent Al-V and Al- Al bonds in the compound [1]. We propose another possibility of the formation of the pseudogap in the DO22 compound using a density functional method. We introduce a Peierls distortions along c-axis of the double-stacked ordered unit cell, we calculate the density of states and check the gap formation. We will apply the mechanism to the other systems with pseudogap. [1] M. Krajc'i and J. Hafner, J. Phys.: Condens. Matter, 14, 1865 (2002).

Aps Meeting Abstracts, Mar 1, 2005

Silicon clathrates are metastable and have been synthesized only when alkaline or alkaline earth ... more Silicon clathrates are metastable and have been synthesized only when alkaline or alkaline earth metal atoms coexist as electron donors or VIa or VIIa atoms coexist as electron acceptors. These guest atoms locate in the cages of the crystals. Now, however, the roll of the guest atoms is unclear in the crystallization processes. We investigate it through investigating the coagulation processes between the cage clusters. We use ab initio electronic structure analysis in real space and the one in momentum space. The formation of dimers between the guest atoms is found to be essential in the synthesis.

Aps Meeting Abstracts, Mar 1, 2010

The low sticking probability of the dissociative adsorption of O2 molecule on Al substrate has be... more The low sticking probability of the dissociative adsorption of O2 molecule on Al substrate has been explained by the nonadiabatic dissociation of the molecule; the dissociated and spin- polarized O2 molecule forms the energy barrier [J. Behler et al., Phys. Rev. B 77, 115421 (2008).] We investigate the detailed charge variations of the atoms in the molecule and in the substrate during the nonadiabatic dissociation. The variation is a fundamental concept in the two-body interactions between the atoms and has been investigated extensively in physics and chemistry; in a simple case of an approaching C and O atom the electron transfers from the C to the O atom to form a CO molecule. So we have investigated the charge variations of the atoms in the H2/Au(111) system, in which the charge has transferred from the H2 molecule to Au(111), of which direction is determined by the electro-negativity difference between the H and Au atoms [S. Takagi et al., J. Phys. Soc. Jpn. 77, 054705 (2008).] We discuss the relation between the instability of the charged and dissociated O2 molecule and the energy barrier of the nonadiabatic O2 dissociation at Al(111).

Aps Meeting Abstracts, Mar 1, 2002

Car and Parrinello (CP) have developed a molecular dynamics method in 1985 to incorporate both th... more Car and Parrinello (CP) have developed a molecular dynamics method in 1985 to incorporate both the electron and atom systems based on the Born-Oppenheimer adiabatic (BOA) approximation for the electron system. Since then the CP method has been used not only for the analyses of dynamical properties of the condensed systems but also for the eigen-value solvers for large sized systems. The BOA approximation has been found to be insufficient for the systems of the chemical reactions. These have been overcome either by introducing the path-integral method into the CP method or by employing the time-dependent density functional (TDDFT) method. The TSDFT method has begun to be practical due to the recent development of the numerical methods such as Suzuki-Trotter expansions. We investigate the dynamical properties of Si clusters using the TDDFT method, compare those calculated by the CP method, and check the validity of the application of the BOA approximation to the CP methods. We use the planewave based TDDFT and CP codes programmed by ourselves.

Aps March Meeting Abstracts, Mar 1, 1996

The existence of magic number has been clarified for rare gas atoms by both theories and experime... more The existence of magic number has been clarified for rare gas atoms by both theories and experiments. The existence is not clear for semiconductors and metals comparing with the rare gas cases. Especially, silicon clusters draw much industrial attention in the current nano scale technology. Cherikowsky et al. footnote J.R.Chelikowsky et al, Phys. Rev. Lett. 62, 292 (1989) have studied the stability of a Si7 cluster of bicapped pentagon with empirical force footnote J.R.Chelikowsky et al, Phys. Rev. Lett. 62, 292 (1989) and ab-initio force footnote N.Bibggeli, Phys. Rev. B 50, 11764 (1994). The is one half of the icosahedral cluster including the central atom of the cluster. The icosahedral cluster is found to be stable even in the metallic glass states. We present the electronic structure analysis of the Si7 cluster. We optimize the structure through the total energy calculation of the clusters with the pseudopotential method in a supercell geometry and discuss the local bonding nature.

Metall Mater Trans a, 1980

The decomposition process of supersaturated solid solution of the Pb-Sb alloys with a small amoun... more The decomposition process of supersaturated solid solution of the Pb-Sb alloys with a small amount of As (˜0.01 wt pct), has been investigated by electrical resistivity measurement. The precipitation process of the Pb-Sb alloys with As is similar to that of the previously reported Pb-As alloys. In the first stage, diffusion of quenched-in excess vacancies accelerates and rate-controls the migration of As and Sb atoms forming an intermediate phase. The second stage is the precipitation of the intermediate phase under the equilibrium vacancy concentration and the third is precipitation of the equilibrium phase. A retardation of reaction in isothermal aging and a partial reversion in isochronal aging appear between the last two stages. The analysis of resistivity change in the Pb-As and Pb-Sb-As alloys shows that the composition and the crystal structure of the intermediate phase are different from those of the equilibrium phase. The mechanism that the preexisted intermediate phase acts as a preferential nucleation site for the equilibrium phase can explain the enhanced precipitation phenomena of the Pb-Sb alloys with trace element As. The reason for the difference in behavior between As and Sb atoms in lead is also discussed.

Group 14 clathrates consisting of Si, Ge, or Sn atoms have been synthesized only when they contai... more Group 14 clathrates consisting of Si, Ge, or Sn atoms have been synthesized only when they contain some specific endohedral atoms. They are Na, K, Rb, or Cs atoms in group 1, Sr or Ba atoms in group 2, and Cl, Br, or I atoms in group 17.[ K.A.Kovnir, et al. Russian Chem. Rev.73,923(2004).] No experiment has been reported on the encapsulation of the earlier row atoms than the atoms mentioned above. We predict the stability of the encapsulation of these atoms using ab initio methods. We evaluate the stability of the guest atom in double caged M2@Si42H36 cluster in the clathrate I, where M is group 1, 2, or 17 atom. The encapsulation of two lithium atoms into one cage and the other is vacant is more stable than the separate encapsulation of lithium atoms into each cage by 0.436eV. The Be2 is the same case and by 0.0859 eV. For sodium case, the separate encapsulation into each cage is more stable by 1.473eV. The strong dimer formation prevents the stabilization of the cage structure. We also evaluate the stabilities in the crystalline states.

Bulletin of the American Physical Society, Mar 17, 2009

Evaluation of the magnetic moments in solids is crucial in the computational physics. The moments... more Evaluation of the magnetic moments in solids is crucial in the computational physics. The moments have been calculated by an atomic sphere approximation or a Voronoi polyhedron approximation. There has been a method to partition the space with the minimum electron charge density surface, called zero flux planes, around each atom. The space is called Bader region. We apply the method to calculate the local magnetic moments of each atom depending on their circumstance using the first principle electronic structure calculation. We obtain the moments from the Bader charges using the up-spin charge and the down-spin charges. We apply the validity of this scheme to the analyses of the spin moments in Fe-N compounds, fcc Fe, and bcc Fe crystals and compare them with the experimental values. For Fe4N, the difference of the moments between Fe(I) and Fe(II) atoms has been larger than that of the Voronoi method and is better agreement with the experimental values than the Voronoi method.

The clathrates I Ba8@Ge46 have been found experimentally to have vacancy defects in the framework... more The clathrates I Ba8@Ge46 have been found experimentally to have vacancy defects in the framework and to form Ba8Ge43. This has been explained by the Zintl-Klemn empirical concept: the inclusion of the barium atoms leads to increase the valence electrons in the framework of the clathrates and the introduction of vacancy defects relaxes the hypervalence of the electrons. We clarify the process of the defect formation by analyzing the electric structure with the first-principle method. We calculate formation energy of a single vacancy in the clathrates in which we use Ceperley-Alder with LDA exchange correlation functional for the pseudopotential of barium atom.[J. Junquera et al. Phys.Rev.B 67,155327(2003)] The energies are 0.09eV for 6c, 0.39eV for 24k, and 0.74eV for 16i sites in the clathrate Ba8@Ge45, although 1.15eV for 6c, 1.31eV for 24k, and 1.70eV for 16i sites in the clathrate Ba8@Si45. The small energy of the 6c site is due to the small binding energy of Ge clathrate. We wi...

Crystals that have silicon clusters as lattice points can be expected to be new artificial materi... more Crystals that have silicon clusters as lattice points can be expected to be new artificial materials as a superconductor and a new type of photoemission elements. Although there has been little information on electronic structures on silicon micro clusters. We report for the first time their electronic structures and the structural differences between fully relaxed structures and symmetry conserving structures

Aps Meeting Abstracts, Mar 1, 2008

We elucidate the origin of the formation analyzing the dissociation process of oxygen molecule on... more We elucidate the origin of the formation analyzing the dissociation process of oxygen molecule on bridge-top-bridge site of Pt(111). The charge state is analyzed by the Bader method together with the spin states of the two oxygen atoms. The charge transfers to the dissociated oxygen molecule from the Au surface. The potential energy variation is in agreement with the energy variation of the separated in distance, charged, and spin polarized oxygen molecules that is calculated with real- space density functional method. Excluding the exchange term in the total energy calculation of the H2/Au system leads to a monotonic increase of the potential energy surface in the dissociation process. The energy barriers in the H2/Mg, H2/Pt, and H2/Au systems are in agreement with the energy variations of the charged, isolated, and separated hydrogen molecules. The barriers appear in late dissociations although no barrier for the nondissociated adsorptions. Their electronegativity differences determine the directions of the transfer in the cases investigated. So we have to reconsider the applicablity of the Pauli repulsion to the barrier formations.

Aps March Meeting Abstracts, Mar 1, 1998

Local density approximation (LDA) in density functional theory (DFT) has succeeded in structural ... more Local density approximation (LDA) in density functional theory (DFT) has succeeded in structural properties of solids with slowly varying charge density. On the other hand, the generalized gradient corrections (GGA's) enable to expand a limitation of LDA to have dependence on the gradient of charge density. However, the superiority of the GGA's with respect to LDA is not clear to

Aps Meeting Abstracts, Mar 1, 2010

Computational material design requires efficient algorithms and high-speed computers to calculate... more Computational material design requires efficient algorithms and high-speed computers to calculate and to predict material properties. The orbital-free first principles calculation (OF- FPC) method, which is a tool for calculating and designing the properties, is an O(N) method and is a powerful tool to study large-scaled systems. We implement a CUFFT routine, which is an FFT library of CUDA (Compute Unified Device Architecture) for GPGPU (General-Purpose Graphics Processing Unit), into our in- house OF-FPC code. We evaluate the computation time to optimize the electron charge density of the sodium crystal systems containing 2, 16, 128, 1024, and 6750 atoms. The GPU-CPU system reduces the time to half of that of the CPU system for the system with 6750 atoms. The GPGPU is effective in accelerating the OF-FPC code.

The fast migration mechanism of the cations in the superionic conductors has been little known up... more The fast migration mechanism of the cations in the superionic conductors has been little known up to now. In the case of α-AgI, the charge states of the Ag atoms and the bonding states between Ag and I atoms during the migration remain to be explained. No explanation has also been given for the origin of both the positions and the asymmetric first peaks of the Ag-I and Ag-Ag pair distribution functions. We investigate the electronic states of AgI using the first principles electronic structure calculations. We use the Bader analysis to evaluate the charges that belong to each atom and obtain the ionicity of the atoms. The stability of the cation pairs in the conductor will be discussed using their binding energies.

Silicon clusters that have a alkali metal in their cage strucutre have possiblity of new artifici... more Silicon clusters that have a alkali metal in their cage strucutre have possiblity of new artificial materials in terms of photoemission effect and superconductivity. One of the candidate is M@Si7 clusters as the compact M@Si clusters. There has been little information on electronic structures on their silicon micro clusters. We report their electronic structures and the structural differences within symmetry conserving condition of icosahedral M@Si7 clusters. We use the first principle norm conserving pseudopotentials using a planewave basis set and a supercell approximation. We discuss the electronic structure differences of M@Si7 clusters.

Aps Meeting Abstracts, 2007

The guest atom displacements in clathrates II have been reported on experimental and theoretical ... more The guest atom displacements in clathrates II have been reported on experimental and theoretical points of views. The recent papers on the displacements are given in the reference [1]. The displacements are found to be about 0.6 åfrom the center of the Si28 cage to the hexagonal ring between the Si28 cages. The binding energies between the guest atoms however have been unknown so far. In the present work we calculate the energies between Na atoms in clathrates II Na2@Si136 and Na24@Si136 with a density functional analysis. We will discuss the cohesion mechanism of the clathrates based on the binding nature between the cations in Zintl phase. [1] H. Takenaka and K. Tsumuraya, Mater. Trans., 47, 63 (2006).

Aps Meeting Abstracts, Mar 1, 1997

Crystals that have silicon clusters as lattice points can be expected to be new artificial materi... more Crystals that have silicon clusters as lattice points can be expected to be new artificial materials as a superconductor and a new type of photoemission elements. There has been little information on electronic structures on silicon micro clusters that has alkali metal as dopant. We report their electronic structures and the structural differences within symmetry conserving condition of dodecahedral M@Si_20 clusters. We use the first principle norm conserving pseudopotential using a planewave basis set and a supercell approximation. We discuss the electronic structure differences of M@Si_20 clusters.

Aps Meeting Abstracts, Mar 1, 2009

The fast migration mechanism of the cations in the superionic conductors has been little known up... more The fast migration mechanism of the cations in the superionic conductors has been little known up to now. In the case of α-AgI, the charge states of the Ag atoms and the bonding states between Ag and I atoms during the migration remain to be explained. No explanation has also been given for the origin of both the positions and the asymmetric first peaks of the Ag-I and Ag-Ag pair distribution functions. We investigate the electronic states of AgI using the first principles electronic structure calculations. We use the Bader analysis to evaluate the charges that belong to each atom and obtain the ionicity of the atoms. The stability of the cation pairs in the conductor will be discussed using their binding energies.

Aps Meeting Abstracts, Mar 1, 2011

The mechanism of the superionic conduction is an unresolved issue in the solid-state physics. The... more The mechanism of the superionic conduction is an unresolved issue in the solid-state physics. The cations are mobile species in alpha -CuI and alpha -AgI crystals. In these conductors, the constituent atoms are ionized. The clarification of the mechanism of the high mobility of the cations needs to investigate the electronic structures in the alpha -CuI crystal. We obtain the dynamically-averaged local (DAL) positions of the mobile copper cations in the crystal from the pair distribution function and the angle distribution functions, which we calculate from the first principles molecular dynamics simulations at 700 K@. The positions predict the existence of a correlation among the cations in the alpha -CuI. The static electronic structure analysis, of the DAL structure, allows us to clarify the correlation. The correlation enables us to clarify the mechanism of the migration and the difference in the electronic structures between the conductors and the ionic crystals.

The pseudogaps in compounds give a unique electronic character in the materials such as the ones ... more The pseudogaps in compounds give a unique electronic character in the materials such as the ones in the skutterudites. The Al3V compound with DO22 structure has also a deep pseudogap that has been explained by the presence of the covalent Al-V and Al- Al bonds in the compound [1]. We propose another possibility of the formation of the pseudogap in the DO22 compound using a density functional method. We introduce a Peierls distortions along c-axis of the double-stacked ordered unit cell, we calculate the density of states and check the gap formation. We will apply the mechanism to the other systems with pseudogap. [1] M. Krajc'i and J. Hafner, J. Phys.: Condens. Matter, 14, 1865 (2002).

Aps Meeting Abstracts, Mar 1, 2005

Silicon clathrates are metastable and have been synthesized only when alkaline or alkaline earth ... more Silicon clathrates are metastable and have been synthesized only when alkaline or alkaline earth metal atoms coexist as electron donors or VIa or VIIa atoms coexist as electron acceptors. These guest atoms locate in the cages of the crystals. Now, however, the roll of the guest atoms is unclear in the crystallization processes. We investigate it through investigating the coagulation processes between the cage clusters. We use ab initio electronic structure analysis in real space and the one in momentum space. The formation of dimers between the guest atoms is found to be essential in the synthesis.

Aps Meeting Abstracts, Mar 1, 2010

The low sticking probability of the dissociative adsorption of O2 molecule on Al substrate has be... more The low sticking probability of the dissociative adsorption of O2 molecule on Al substrate has been explained by the nonadiabatic dissociation of the molecule; the dissociated and spin- polarized O2 molecule forms the energy barrier [J. Behler et al., Phys. Rev. B 77, 115421 (2008).] We investigate the detailed charge variations of the atoms in the molecule and in the substrate during the nonadiabatic dissociation. The variation is a fundamental concept in the two-body interactions between the atoms and has been investigated extensively in physics and chemistry; in a simple case of an approaching C and O atom the electron transfers from the C to the O atom to form a CO molecule. So we have investigated the charge variations of the atoms in the H2/Au(111) system, in which the charge has transferred from the H2 molecule to Au(111), of which direction is determined by the electro-negativity difference between the H and Au atoms [S. Takagi et al., J. Phys. Soc. Jpn. 77, 054705 (2008).] We discuss the relation between the instability of the charged and dissociated O2 molecule and the energy barrier of the nonadiabatic O2 dissociation at Al(111).

Aps Meeting Abstracts, Mar 1, 2002

Car and Parrinello (CP) have developed a molecular dynamics method in 1985 to incorporate both th... more Car and Parrinello (CP) have developed a molecular dynamics method in 1985 to incorporate both the electron and atom systems based on the Born-Oppenheimer adiabatic (BOA) approximation for the electron system. Since then the CP method has been used not only for the analyses of dynamical properties of the condensed systems but also for the eigen-value solvers for large sized systems. The BOA approximation has been found to be insufficient for the systems of the chemical reactions. These have been overcome either by introducing the path-integral method into the CP method or by employing the time-dependent density functional (TDDFT) method. The TSDFT method has begun to be practical due to the recent development of the numerical methods such as Suzuki-Trotter expansions. We investigate the dynamical properties of Si clusters using the TDDFT method, compare those calculated by the CP method, and check the validity of the application of the BOA approximation to the CP methods. We use the planewave based TDDFT and CP codes programmed by ourselves.

Aps March Meeting Abstracts, Mar 1, 1996

The existence of magic number has been clarified for rare gas atoms by both theories and experime... more The existence of magic number has been clarified for rare gas atoms by both theories and experiments. The existence is not clear for semiconductors and metals comparing with the rare gas cases. Especially, silicon clusters draw much industrial attention in the current nano scale technology. Cherikowsky et al. footnote J.R.Chelikowsky et al, Phys. Rev. Lett. 62, 292 (1989) have studied the stability of a Si7 cluster of bicapped pentagon with empirical force footnote J.R.Chelikowsky et al, Phys. Rev. Lett. 62, 292 (1989) and ab-initio force footnote N.Bibggeli, Phys. Rev. B 50, 11764 (1994). The is one half of the icosahedral cluster including the central atom of the cluster. The icosahedral cluster is found to be stable even in the metallic glass states. We present the electronic structure analysis of the Si7 cluster. We optimize the structure through the total energy calculation of the clusters with the pseudopotential method in a supercell geometry and discuss the local bonding nature.

Metall Mater Trans a, 1980

The decomposition process of supersaturated solid solution of the Pb-Sb alloys with a small amoun... more The decomposition process of supersaturated solid solution of the Pb-Sb alloys with a small amount of As (˜0.01 wt pct), has been investigated by electrical resistivity measurement. The precipitation process of the Pb-Sb alloys with As is similar to that of the previously reported Pb-As alloys. In the first stage, diffusion of quenched-in excess vacancies accelerates and rate-controls the migration of As and Sb atoms forming an intermediate phase. The second stage is the precipitation of the intermediate phase under the equilibrium vacancy concentration and the third is precipitation of the equilibrium phase. A retardation of reaction in isothermal aging and a partial reversion in isochronal aging appear between the last two stages. The analysis of resistivity change in the Pb-As and Pb-Sb-As alloys shows that the composition and the crystal structure of the intermediate phase are different from those of the equilibrium phase. The mechanism that the preexisted intermediate phase acts as a preferential nucleation site for the equilibrium phase can explain the enhanced precipitation phenomena of the Pb-Sb alloys with trace element As. The reason for the difference in behavior between As and Sb atoms in lead is also discussed.

Group 14 clathrates consisting of Si, Ge, or Sn atoms have been synthesized only when they contai... more Group 14 clathrates consisting of Si, Ge, or Sn atoms have been synthesized only when they contain some specific endohedral atoms. They are Na, K, Rb, or Cs atoms in group 1, Sr or Ba atoms in group 2, and Cl, Br, or I atoms in group 17.[ K.A.Kovnir, et al. Russian Chem. Rev.73,923(2004).] No experiment has been reported on the encapsulation of the earlier row atoms than the atoms mentioned above. We predict the stability of the encapsulation of these atoms using ab initio methods. We evaluate the stability of the guest atom in double caged M2@Si42H36 cluster in the clathrate I, where M is group 1, 2, or 17 atom. The encapsulation of two lithium atoms into one cage and the other is vacant is more stable than the separate encapsulation of lithium atoms into each cage by 0.436eV. The Be2 is the same case and by 0.0859 eV. For sodium case, the separate encapsulation into each cage is more stable by 1.473eV. The strong dimer formation prevents the stabilization of the cage structure. We also evaluate the stabilities in the crystalline states.

Bulletin of the American Physical Society, Mar 17, 2009

Evaluation of the magnetic moments in solids is crucial in the computational physics. The moments... more Evaluation of the magnetic moments in solids is crucial in the computational physics. The moments have been calculated by an atomic sphere approximation or a Voronoi polyhedron approximation. There has been a method to partition the space with the minimum electron charge density surface, called zero flux planes, around each atom. The space is called Bader region. We apply the method to calculate the local magnetic moments of each atom depending on their circumstance using the first principle electronic structure calculation. We obtain the moments from the Bader charges using the up-spin charge and the down-spin charges. We apply the validity of this scheme to the analyses of the spin moments in Fe-N compounds, fcc Fe, and bcc Fe crystals and compare them with the experimental values. For Fe4N, the difference of the moments between Fe(I) and Fe(II) atoms has been larger than that of the Voronoi method and is better agreement with the experimental values than the Voronoi method.

The clathrates I Ba8@Ge46 have been found experimentally to have vacancy defects in the framework... more The clathrates I Ba8@Ge46 have been found experimentally to have vacancy defects in the framework and to form Ba8Ge43. This has been explained by the Zintl-Klemn empirical concept: the inclusion of the barium atoms leads to increase the valence electrons in the framework of the clathrates and the introduction of vacancy defects relaxes the hypervalence of the electrons. We clarify the process of the defect formation by analyzing the electric structure with the first-principle method. We calculate formation energy of a single vacancy in the clathrates in which we use Ceperley-Alder with LDA exchange correlation functional for the pseudopotential of barium atom.[J. Junquera et al. Phys.Rev.B 67,155327(2003)] The energies are 0.09eV for 6c, 0.39eV for 24k, and 0.74eV for 16i sites in the clathrate Ba8@Ge45, although 1.15eV for 6c, 1.31eV for 24k, and 1.70eV for 16i sites in the clathrate Ba8@Si45. The small energy of the 6c site is due to the small binding energy of Ge clathrate. We wi...

Crystals that have silicon clusters as lattice points can be expected to be new artificial materi... more Crystals that have silicon clusters as lattice points can be expected to be new artificial materials as a superconductor and a new type of photoemission elements. Although there has been little information on electronic structures on silicon micro clusters. We report for the first time their electronic structures and the structural differences between fully relaxed structures and symmetry conserving structures

Aps Meeting Abstracts, Mar 1, 2008

We elucidate the origin of the formation analyzing the dissociation process of oxygen molecule on... more We elucidate the origin of the formation analyzing the dissociation process of oxygen molecule on bridge-top-bridge site of Pt(111). The charge state is analyzed by the Bader method together with the spin states of the two oxygen atoms. The charge transfers to the dissociated oxygen molecule from the Au surface. The potential energy variation is in agreement with the energy variation of the separated in distance, charged, and spin polarized oxygen molecules that is calculated with real- space density functional method. Excluding the exchange term in the total energy calculation of the H2/Au system leads to a monotonic increase of the potential energy surface in the dissociation process. The energy barriers in the H2/Mg, H2/Pt, and H2/Au systems are in agreement with the energy variations of the charged, isolated, and separated hydrogen molecules. The barriers appear in late dissociations although no barrier for the nondissociated adsorptions. Their electronegativity differences determine the directions of the transfer in the cases investigated. So we have to reconsider the applicablity of the Pauli repulsion to the barrier formations.

Aps March Meeting Abstracts, Mar 1, 1998

Local density approximation (LDA) in density functional theory (DFT) has succeeded in structural ... more Local density approximation (LDA) in density functional theory (DFT) has succeeded in structural properties of solids with slowly varying charge density. On the other hand, the generalized gradient corrections (GGA's) enable to expand a limitation of LDA to have dependence on the gradient of charge density. However, the superiority of the GGA's with respect to LDA is not clear to

Aps Meeting Abstracts, Mar 1, 2010

Computational material design requires efficient algorithms and high-speed computers to calculate... more Computational material design requires efficient algorithms and high-speed computers to calculate and to predict material properties. The orbital-free first principles calculation (OF- FPC) method, which is a tool for calculating and designing the properties, is an O(N) method and is a powerful tool to study large-scaled systems. We implement a CUFFT routine, which is an FFT library of CUDA (Compute Unified Device Architecture) for GPGPU (General-Purpose Graphics Processing Unit), into our in- house OF-FPC code. We evaluate the computation time to optimize the electron charge density of the sodium crystal systems containing 2, 16, 128, 1024, and 6750 atoms. The GPU-CPU system reduces the time to half of that of the CPU system for the system with 6750 atoms. The GPGPU is effective in accelerating the OF-FPC code.

The fast migration mechanism of the cations in the superionic conductors has been little known up... more The fast migration mechanism of the cations in the superionic conductors has been little known up to now. In the case of α-AgI, the charge states of the Ag atoms and the bonding states between Ag and I atoms during the migration remain to be explained. No explanation has also been given for the origin of both the positions and the asymmetric first peaks of the Ag-I and Ag-Ag pair distribution functions. We investigate the electronic states of AgI using the first principles electronic structure calculations. We use the Bader analysis to evaluate the charges that belong to each atom and obtain the ionicity of the atoms. The stability of the cation pairs in the conductor will be discussed using their binding energies.

Silicon clusters that have a alkali metal in their cage strucutre have possiblity of new artifici... more Silicon clusters that have a alkali metal in their cage strucutre have possiblity of new artificial materials in terms of photoemission effect and superconductivity. One of the candidate is M@Si7 clusters as the compact M@Si clusters. There has been little information on electronic structures on their silicon micro clusters. We report their electronic structures and the structural differences within symmetry conserving condition of icosahedral M@Si7 clusters. We use the first principle norm conserving pseudopotentials using a planewave basis set and a supercell approximation. We discuss the electronic structure differences of M@Si7 clusters.

Aps Meeting Abstracts, 2007

The guest atom displacements in clathrates II have been reported on experimental and theoretical ... more The guest atom displacements in clathrates II have been reported on experimental and theoretical points of views. The recent papers on the displacements are given in the reference [1]. The displacements are found to be about 0.6 åfrom the center of the Si28 cage to the hexagonal ring between the Si28 cages. The binding energies between the guest atoms however have been unknown so far. In the present work we calculate the energies between Na atoms in clathrates II Na2@Si136 and Na24@Si136 with a density functional analysis. We will discuss the cohesion mechanism of the clathrates based on the binding nature between the cations in Zintl phase. [1] H. Takenaka and K. Tsumuraya, Mater. Trans., 47, 63 (2006).

Aps Meeting Abstracts, Mar 1, 1997

Crystals that have silicon clusters as lattice points can be expected to be new artificial materi... more Crystals that have silicon clusters as lattice points can be expected to be new artificial materials as a superconductor and a new type of photoemission elements. There has been little information on electronic structures on silicon micro clusters that has alkali metal as dopant. We report their electronic structures and the structural differences within symmetry conserving condition of dodecahedral M@Si_20 clusters. We use the first principle norm conserving pseudopotential using a planewave basis set and a supercell approximation. We discuss the electronic structure differences of M@Si_20 clusters.

Aps Meeting Abstracts, Mar 1, 2009

The fast migration mechanism of the cations in the superionic conductors has been little known up... more The fast migration mechanism of the cations in the superionic conductors has been little known up to now. In the case of α-AgI, the charge states of the Ag atoms and the bonding states between Ag and I atoms during the migration remain to be explained. No explanation has also been given for the origin of both the positions and the asymmetric first peaks of the Ag-I and Ag-Ag pair distribution functions. We investigate the electronic states of AgI using the first principles electronic structure calculations. We use the Bader analysis to evaluate the charges that belong to each atom and obtain the ionicity of the atoms. The stability of the cation pairs in the conductor will be discussed using their binding energies.

Aps Meeting Abstracts, Mar 1, 2011

The mechanism of the superionic conduction is an unresolved issue in the solid-state physics. The... more The mechanism of the superionic conduction is an unresolved issue in the solid-state physics. The cations are mobile species in alpha -CuI and alpha -AgI crystals. In these conductors, the constituent atoms are ionized. The clarification of the mechanism of the high mobility of the cations needs to investigate the electronic structures in the alpha -CuI crystal. We obtain the dynamically-averaged local (DAL) positions of the mobile copper cations in the crystal from the pair distribution function and the angle distribution functions, which we calculate from the first principles molecular dynamics simulations at 700 K@. The positions predict the existence of a correlation among the cations in the alpha -CuI. The static electronic structure analysis, of the DAL structure, allows us to clarify the correlation. The correlation enables us to clarify the mechanism of the migration and the difference in the electronic structures between the conductors and the ionic crystals.