The Experts below are selected from a list of 135 Experts worldwide ranked by ideXlab platform
Hiroshi Nakatsuji - One of the best experts on this subject based on the ideXlab platform.
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Spin-orbit effect on the magnetic shielding constant: niobium hexahalides and titanium tetrahalides
Chemical Physics Letters, 1997Co-Authors: Hiroshi Nakatsuji, Takahito NakajimaAbstract:Abstract The 93 Nb and 47 Ti NMR chemical shifts of niobium hexahalides and titanium tetrahalides are studied theoretically by the ab initio UHF/finite perturbation method including the spin-orbit (SO) interaction. The calculated chemical shifts agree well with experiment for both the Nb and Ti compounds. In contrast to the halides of main-group elements studied previously, the SO effect is generally small for early transition metal halides. The origin of the chemical shifts lies in the d-orbital contribution of the Paramagnetic Term and is due to the d-d ∗ excitation mechanism. Soft d-orbitals adsorb the SO effect, leaving only a small net spin-orbit effect. The chemical shift shows a monotonic downfield shift as the halogen ligand becomes heavier (inverse halogen dependence), in contrast to the normal halogen dependence observed for the halides of main-group elements. It is expected that such a result is common to other transition metal halides in which the transition metal atom has an open d subshell.
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Spin-orbit effect on the magnetic shielding constant using the ab initio UHF method. Electronic mechanism in the aluminum compounds, A1X4− (X = H, F, Cl, Br and I)
Chemical Physics Letters, 1996Co-Authors: Hiroshi Nakatsuji, Masahiko Hada, T. Tejima, Tohru Nakajima, Manabu SugimotoAbstract:Abstract The 27 Al NMR chemical shifts of the compounds A1X 4 − (X = H, F, Cl, Br and I) are studied theoretically by the ab initio UHF/finite perturbation (FP) method including a previously propsed spin-orbit (SO) interaction. When the SO interaction is included, the calculated chemical sshifts agree well with experiment. The SO effects become large in the heavier halogen compounds, AlBr 4 − .and AlI 4 − . The Paramagnetic Term and the SO Term are important in the chemical shifts of these compounds. The Paramagnetic Term is governed by the Al valence p electron mechanism and the SO Term arises from the Fermi contact interaction in the Al valence s-orbital. The twofold halogen dependences, namely the normal halogen dependence and the inverse halogen dependence, observed for those compounds arise from the SO effect and the p-electron mechanism, respectively.
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Spin—orbit effect on the magnetic shielding constant using the ab initio UHF method: silicon tetrahalides
Chemical Physics Letters, 1995Co-Authors: Hiroshi Nakatsuji, Masahiko Hada, Takahito Nakajima, Hajime Takashima, Shinji TanakaAbstract:Abstract The 29Si NMR chemical shifts of silane, SiH4, and silicon tetrahalides, SiX4 (X = F, Cl, Br and I) and SiXI3 (X = Cl and Br), are calculated by the ab initio unrestricted Hartree-Fock/finite perturbation method including the spin-orbit (SO) interaction proposed previously. The SO effect is included through the effective core potentials for the halogens. The chemical shifts calculated with the SO effects show good agreement with experiment for all the compounds studied. The SO effects of the halogen ligands, especially of bromine and iodine, are large and move the chemical shift to higher magnetic field. The inverse halogen dependence on the substitution of F by Cl is derived from the Paramagnetic Term, but the normal halogen dependence on the substitution from Cl to I is caused mainly by the SO effect.
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Theoretical study on metal NMR chemical shifts : germanium compounds
International Journal of Quantum Chemistry, 1994Co-Authors: Hiroshi Nakatsuji, T. NakaoAbstract:Germanium chemical shifts were studied theoretically by the ab initio molecular orbital method. The compounds studied were GeMe4−xClx and GeMe4−xHx(x = 0–4). The calculated values of the germanium chemical shifts agreed well with the available experimental values. The germanium chemical shift is due to the p-electron mechanism that reflects the ligand electronic effect on the p-p* excitation Term in the second-order Paramagnetic Term. For GeMe4−xHx, the chemical shift is almost linear to the number of the ligand, x. On the other hand, a U-shaped dependence is predicted for the chemical shifts of the GeMe4−xClx series and is shown to be caused by the strong and nonadditive electron-withdrawing ability of the Cl ligand. The diamagnetic contribution is relatively small for the chemical shift and is deTermined solely by a structural factor. © 1994 John Wiley & Sons, Inc.
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Electronic Mechanisms of Metal Chemical Shifts from Ab Initio Theory
Nuclear Magnetic Shieldings and Molecular Structure, 1993Co-Authors: Hiroshi NakatsujiAbstract:A progress report on the study of the mechanisms of the metal chemical shifts carried out in this laboratory is given. The major mechanism is understood by the atomic electron configuration of the central metal: p- and d-mechanisms for d10s1–2p0 metal complexs, d-excitation mechanism for d n metal complexes, and p-excitation mechanism for s2p2 metal complexes. Though the Paramagnetic Term is the origin for most complexes, the chemical shifts of the Ga and In (s2p1) halides are primarily deTermined by the diamagnetic Term, and therefore by the structural factors (geometry and nuclear charges) alone.
H. Krenn - One of the best experts on this subject based on the ideXlab platform.
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A ferromagnetic (porous silicon/metal)-nanocomposite with an additional Paramagnetic behavior
Physica E: Low-dimensional Systems and Nanostructures, 2008Co-Authors: Klemens Rumpf, Petra Granitzer, Peter Pölt, Sanja Simic, M. Hofmayer, H. KrennAbstract:Investigations on a nanostructured metal/semiconductor hybrid system show a novel magnetic behavior with a spin-magnetism at low magnetic fields and an additional Paramagnetic Term at higher fields. The system is composed of a porous silicon (PS) matrix formed by anodization of an n-type silicon wafer with electrochemically deposited metal-structures. The morphology of the membrane is tuneable by the anodization conditions, but the metal deposition within the channels of the template can also be modified by changing the galvanic parameters of the metal-loading procedure. Both the variation of the template (pore-diameter, pore-distance) and the adjustment of the metal-filling (spatial distribution along the channels, shape of the precipitations) enable selective modification of the magnetic properties of the nanocomposite system. The geometry of the precipitated metal-structures, which vary between spheres, ellipsoids and wires as well as their mutual arrangement, deTermines the magnetic behavior (coercivity, squareness) at magnetic fields beneath the saturation magnetization of the deposited metal. At higher magnetic fields a subsequent non-saturating Paramagnetic Term occurs which is due to orbital currents in silicon. Both properties together, the spin-magnetism and the additionally appearing orbital magnetism form a novel magnetic behavior, characteristic for the introduced hybrid nanocomposite.
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Porous Silicon/Metal Hybrid System With Ferro and Paramagnetic Behavior
IEEE Transactions on Magnetics, 2008Co-Authors: Klemens Rumpf, Petra Granitzer, H. KrennAbstract:Fabricated ferromagnetic hybrid systems consisting of a porous silicon (PS) matrix with incorporated metal nanostructures exhibit magnetic properties which can be distinguished in two ranges. A first one is related to magnetic fields below the saturation magnetization of the deposited metal and a second one to higher magnetic fields. Considering the low field region the samples show magnetic characteristics due to the metal-precipitations (geometry, distribution, kind of metal) tunable by the deposition parameters. At higher fields an additional novel non-saturating Term is observed which is dependent on the temperature and differs in strength between Ni and Co. In the frame of this work this additional Paramagnetic Term is experimentally investigated.
Balazs Dora - One of the best experts on this subject based on the ideXlab platform.
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nuclear spin lattice relaxation time in tap and the knight shift of weyl semimetals
Physical Review B, 2019Co-Authors: Zoltan Okvatovity, H Yasuoka, M Baenitz, F Simon, Balazs DoraAbstract:We first analyze the recent experimental data on the nuclear spin-lattice relaxation rate of the Weyl semimetal TaP. We argue that its nonmonotonic temperature dependence is explained by the temperature-dependent chemical potential of Weyl fermions. We also develop the theory of the Knight shift in Weyl semimetals, which contains two counteracting Terms. The diamagnetic Term follows $\ensuremath{-}ln[W/max(|\ensuremath{\mu}|,{k}_{B}T)]$ with $W,\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}$, and $T$ being the high-energy cutoff, chemical potential, and temperature, respectively, and is always negative. The Paramagnetic Term scales with $\ensuremath{\mu}$ and changes sign depending on the doping level. Altogether, the Knight shift is predicted to vanish or even change sign upon changing the doping or the temperature, making it a sensitive tool to identify Weyl points. We also calculate the Korringa relation for Weyl semimetals which shows an unusual energy dependence rather than being constant as expected for a noninteracting Fermi system.
T. Nakao - One of the best experts on this subject based on the ideXlab platform.
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Theoretical study on metal NMR chemical shifts : germanium compounds
International Journal of Quantum Chemistry, 1994Co-Authors: Hiroshi Nakatsuji, T. NakaoAbstract:Germanium chemical shifts were studied theoretically by the ab initio molecular orbital method. The compounds studied were GeMe4−xClx and GeMe4−xHx(x = 0–4). The calculated values of the germanium chemical shifts agreed well with the available experimental values. The germanium chemical shift is due to the p-electron mechanism that reflects the ligand electronic effect on the p-p* excitation Term in the second-order Paramagnetic Term. For GeMe4−xHx, the chemical shift is almost linear to the number of the ligand, x. On the other hand, a U-shaped dependence is predicted for the chemical shifts of the GeMe4−xClx series and is shown to be caused by the strong and nonadditive electron-withdrawing ability of the Cl ligand. The diamagnetic contribution is relatively small for the chemical shift and is deTermined solely by a structural factor. © 1994 John Wiley & Sons, Inc.
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Theoretical study on metal NMR chemical shifts: electronic mechanism of the tin chemical shift
The Journal of Physical Chemistry, 1992Co-Authors: Hiroshi Nakatsuji, T. Inoue, T. NakaoAbstract:Sn chemical shifts of the complexes SnMe 4-x H x and SnMe 4-x Cl x (x=0-4) are studied theoretically by an ab initio molecular orbital method using larger basis sets than our previous ones. The calculated values of the Sn chemical shifts agree reasonably with the experimental values. The electronic mechanism of the Sn chemical shifts is analyzed. The Sn chemical shifts are mainly governed by the Sn valence p AO contribution to the Paramagnetic Term. The diamagnetic Term is small and deTermined solely by the structural factor
Takahito Nakajima - One of the best experts on this subject based on the ideXlab platform.
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Spin-orbit effect on the magnetic shielding constant: niobium hexahalides and titanium tetrahalides
Chemical Physics Letters, 1997Co-Authors: Hiroshi Nakatsuji, Takahito NakajimaAbstract:Abstract The 93 Nb and 47 Ti NMR chemical shifts of niobium hexahalides and titanium tetrahalides are studied theoretically by the ab initio UHF/finite perturbation method including the spin-orbit (SO) interaction. The calculated chemical shifts agree well with experiment for both the Nb and Ti compounds. In contrast to the halides of main-group elements studied previously, the SO effect is generally small for early transition metal halides. The origin of the chemical shifts lies in the d-orbital contribution of the Paramagnetic Term and is due to the d-d ∗ excitation mechanism. Soft d-orbitals adsorb the SO effect, leaving only a small net spin-orbit effect. The chemical shift shows a monotonic downfield shift as the halogen ligand becomes heavier (inverse halogen dependence), in contrast to the normal halogen dependence observed for the halides of main-group elements. It is expected that such a result is common to other transition metal halides in which the transition metal atom has an open d subshell.
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Spin—orbit effect on the magnetic shielding constant using the ab initio UHF method: silicon tetrahalides
Chemical Physics Letters, 1995Co-Authors: Hiroshi Nakatsuji, Masahiko Hada, Takahito Nakajima, Hajime Takashima, Shinji TanakaAbstract:Abstract The 29Si NMR chemical shifts of silane, SiH4, and silicon tetrahalides, SiX4 (X = F, Cl, Br and I) and SiXI3 (X = Cl and Br), are calculated by the ab initio unrestricted Hartree-Fock/finite perturbation method including the spin-orbit (SO) interaction proposed previously. The SO effect is included through the effective core potentials for the halogens. The chemical shifts calculated with the SO effects show good agreement with experiment for all the compounds studied. The SO effects of the halogen ligands, especially of bromine and iodine, are large and move the chemical shift to higher magnetic field. The inverse halogen dependence on the substitution of F by Cl is derived from the Paramagnetic Term, but the normal halogen dependence on the substitution from Cl to I is caused mainly by the SO effect.
