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Haydn Chen - One of the best experts on this subject based on the ideXlab platform.
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improvement of the spin polarized self consistent charge Extended Huckel tight binding method
Materials Chemistry and Physics, 2000Co-Authors: Michihide Kitamura, Kanryu Inoue, Haydn ChenAbstract:Abstract The spin-polarized self-consistent-charge Extended Huckel tight-binding (SP-SCC-XHTB) method has been developed by authors to study the electronic structures of rutile-type transition metal dioxides, MO2, with both the nonmagnetic and magnetic phases. This method has been used to successfully predict the electronic structures of nonmagnetic (n) MO2’s with M =Ti, V, Nb, Ta, Cr and ferromagnetic (f) CrO2, but is inadequate to predict the value of the energy gap of a semiconductive n-MnO2. The SP-SCC-XHTB band structure calculation, which includes all the relativistic effects in a first principal manner, has only one empirical parameter on the evaluation of the matrix elements of the non-relativistic Hamiltonian H0. In this paper, the SP-SCC-XHTB method is improved so as to evaluate the matrix elements of the H0 in a more appropriate manner. The band structure calculations are carried out for the n-MO2’s with M =Ti, V, Nb, Ta, Cr and Mn, the f-CrO2 and the af-MnO2. With the improvement it is shown that the SP-SCC-IXHTB band structure calculations give reasonable results for the electronic structures of all the MO2’s considered in the present paper.
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electronic structures of transition metal dioxides studied by the spin polarized self consistent charge Extended Huckel tight binding method
Materials Chemistry and Physics, 1998Co-Authors: Michihide Kitamura, Kanryu Inoue, Haydn ChenAbstract:Abstract Band theory based on the spin-polarized self-consistent-charge Extended Huckel tight-binding (SP-SCC-XHTB) method, which includes all the relativistic effects and the spin-polarized self-consistent-field (SP-SCF) atomic-structure calculation based on the Hartree-Fock-Slater method, has been applied to the electronic-structure calculations of tetragonal rutile-type MO2s, such as nonmagnetic (n) TiO2, VO2, NbO2, TaO2, CrO2, MnO2, ferromagnetic (f) CrO2 and antiferromagnetic (af) MnO2. It is shown that the calculations are consistent with the experimental observations for all systems except the case of MnO2. It is demonstrated that the semiconductive nature of MnO2 can be explained by adding an assumption that three electrons in the Mn t2g orbital are localized in the crystal into the SP-SCC-XHTB band-structure calculation.
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electronic structure of barium titanate studies by the Extended Huckel tight binding method
Journal of Applied Physics, 1994Co-Authors: M Holma, M Kitamura, Haydn ChenAbstract:The electronic structure of barium titanate is determined according to the Extended Huckel tight‐binding method using atomic data based on a self‐consistent‐field calculation. The effects of the phase transition on the partial density of states are studied. The electronic contribution to the phase stability of the compound is calculated from the total density of states. The tetragonal phase is found to be stable as compared to the cubic phase. The density of states is compared with available x‐ray photoemission spectra and is found to be in agreement with some features in experimental results.
Michihide Kitamura - One of the best experts on this subject based on the ideXlab platform.
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improvement of the spin polarized self consistent charge Extended Huckel tight binding method
Materials Chemistry and Physics, 2000Co-Authors: Michihide Kitamura, Kanryu Inoue, Haydn ChenAbstract:Abstract The spin-polarized self-consistent-charge Extended Huckel tight-binding (SP-SCC-XHTB) method has been developed by authors to study the electronic structures of rutile-type transition metal dioxides, MO2, with both the nonmagnetic and magnetic phases. This method has been used to successfully predict the electronic structures of nonmagnetic (n) MO2’s with M =Ti, V, Nb, Ta, Cr and ferromagnetic (f) CrO2, but is inadequate to predict the value of the energy gap of a semiconductive n-MnO2. The SP-SCC-XHTB band structure calculation, which includes all the relativistic effects in a first principal manner, has only one empirical parameter on the evaluation of the matrix elements of the non-relativistic Hamiltonian H0. In this paper, the SP-SCC-XHTB method is improved so as to evaluate the matrix elements of the H0 in a more appropriate manner. The band structure calculations are carried out for the n-MO2’s with M =Ti, V, Nb, Ta, Cr and Mn, the f-CrO2 and the af-MnO2. With the improvement it is shown that the SP-SCC-IXHTB band structure calculations give reasonable results for the electronic structures of all the MO2’s considered in the present paper.
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electronic structures of transition metal dioxides studied by the spin polarized self consistent charge Extended Huckel tight binding method
Materials Chemistry and Physics, 1998Co-Authors: Michihide Kitamura, Kanryu Inoue, Haydn ChenAbstract:Abstract Band theory based on the spin-polarized self-consistent-charge Extended Huckel tight-binding (SP-SCC-XHTB) method, which includes all the relativistic effects and the spin-polarized self-consistent-field (SP-SCF) atomic-structure calculation based on the Hartree-Fock-Slater method, has been applied to the electronic-structure calculations of tetragonal rutile-type MO2s, such as nonmagnetic (n) TiO2, VO2, NbO2, TaO2, CrO2, MnO2, ferromagnetic (f) CrO2 and antiferromagnetic (af) MnO2. It is shown that the calculations are consistent with the experimental observations for all systems except the case of MnO2. It is demonstrated that the semiconductive nature of MnO2 can be explained by adding an assumption that three electrons in the Mn t2g orbital are localized in the crystal into the SP-SCC-XHTB band-structure calculation.
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electronic structure calculations of perovskite type oxides using the self consistent charge Extended Huckel tight binding method
Ferroelectrics, 1998Co-Authors: Michihide Kitamura, Hayden ChenAbstract:Abstract Electronic structures of nine cubic perovskite-type oxides ABO3's including SrTiO3, SrZrO3, SrHfO3, BaTiO3, BaZrO3, BaHfO3, PbTiO3, PbZrO3 and PbHfO3 were calculated using a band theory based on the self-consistent-charge Extended Huckel tight-binding (SCC-XHTB) method incorporating the relativistic effects except for the spin-orbit interaction in order to examine how the electronic structure changes due to the substitution of the A or B site atom. Moreover, calculations were also made for the tetragonal PbTiO3 to study the electronic structural changes due to the structural change from the cubic phase to the tetragonal one. It is shown that the upper valence band of all the ABO3's considered in the present paper consists of the 2p orbital of oxygen mixed with the d valence electrons of the B atom. The shape remains nearly the same in spite of the A or B site substitution. For the conduction band, it is shown that the bottom of which is made up from the ndt 2g band of the B atom for SrTiO3, SrZrO...
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elastic properties of semiconductors studied by Extended Huckel theory
Physical Review B, 1992Co-Authors: Michihide Kitamura, Shinji Muramatsu, Walter A HarrisonAbstract:For thirty diamond- and zinc-blende-structure semiconductors, the elastic shear constant (c 11 -c 12 )/2, polarity α p , effective atomic charge Z * , transfer parameter β, and transverse charge e T * are calculated from band-structure calculations based on the Extended Huckel tight-binding method. The results are compared with previous theoretical calculations and experiment
Avik W Ghosh - One of the best experts on this subject based on the ideXlab platform.
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Extended Huckel theory for band structure chemistry and transport i carbon nanotubes
Journal of Applied Physics, 2006Co-Authors: Diego Kienle, Jorge I Cerda, Avik W GhoshAbstract:We describe a semiempirical atomic basis Extended Huckel theoretical (EHT) technique that can be used to calculate bulk band structure, surface density of states, electronic transmission, and interfacial chemistry of various materials within the same computational platform. We apply this method to study multiple technologically important systems, starting with carbon nanotubes and their interfaces and silicon-based heterostructures in our follow-up paper [D. Kienle et al., J. Appl. Phys. 100, 043715 (2006), following paper]. We find that when it comes to quantum transport through interesting, complex heterostructures including gas molecules adsorbed on nanotubes, the Huckel band structure offers a fair and practical compromise between orthogonal tight-binding theories with limited transferability between environments under large distortion and density functional theories that are computationally quite expensive for the same purpose.
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Extended Huckel theory for band structure chemistry and transport ii silicon
Journal of Applied Physics, 2006Co-Authors: Diego Kienle, Jorge I Cerda, Kirk H Bevan, Gengchiau Liang, Lutfe Siddiqui, Avik W GhoshAbstract:In this second paper, we develop transferable semiempirical Extended Huckel theoretical (EHT) parameters for the electronic structure of another technologically important material, namely, silicon. The EHT parameters are optimized to experimental target values of the band dispersion of bulk silicon. We quantitatively benchmark our parameters to bulk electronic properties such as band edge energies and locations, effective masses, and spin-orbit coupling parameters, competitive with a nearest-neighbor sp3d5s* orthogonal tight-binding model for silicon of T. Boykin et al. [Phys. Rev. B 69, 115201 (2004)] that has been widely used to model silicon-based devices (see, e.g., A. Rahman et al. [Jpn. J. Appl. Phys. Part I 44, 2187 (2005)] and J. Wang et al. [Appl. Phys. Lett. 86, 093113 (2005)]). The transferability of the parameters is checked for multiple physical and chemical configurations, specifically, two different reconstructed surfaces, Si(100)-(2×1) and Si(111)-(2×1). The robustness of the parameters to...
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Extended Huckel theory for bandstructure chemistry and transport ii silicon
arXiv: Materials Science, 2006Co-Authors: Diego Kienle, Jorge I Cerda, Kirk H Bevan, Gengchiau Liang, Lutfe Siddiqui, Avik W GhoshAbstract:In this second paper, we develop transferable semi-empirical parameters for the technologically important material, silicon, using Extended Huckel Theory (EHT) to calculate its electronic structure. The EHT-parameters areoptimized to experimental target values of the band dispersion of bulk-silicon. We obtain a very good quantitative match to the bandstructure characteristics such as bandedges and effective masses, which are competitive with the values obtained within an $sp^3 d^5 s^*$ orthogonal-tight binding model for silicon. The transferability of the parameters is investigated applying them to different physical and chemical environments by calculating the bandstructure of two reconstructed surfaces with different orientations: Si(100) (2x1) and Si(111) (2x1). The reproduced $\pi$- and $\pi^*$-surface bands agree in part quantitatively with DFT-GW calculations and PES/IPES experiments demonstrating their robustness to environmental changes. We further apply the silicon parameters to describe the 1D band dispersion of a unrelaxed rectangular silicon nanowire (SiNW) and demonstrate the EHT-approach of surface passivation using hydrogen. Our EHT-parameters thus provide a quantitative model of bulk-silicon and silicon-based materials such as contacts and surfaces, which are essential ingredients towards a quantitative quantum transport simulation through silicon-based heterostructures.
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Extended Huckel theory for bandstructure chemistry and transport i carbon nanotubes
arXiv: Materials Science, 2006Co-Authors: Diego Kienle, Jorge I Cerda, Avik W GhoshAbstract:We describe a semi-empirical atomic basis Extended H\"uckel Theoretical (EHT) technique that can be used to calculate bulk bandstructure, surface density of states, electronic transmission and interfacial chemistry of various materials within the same computational platform. We apply this method to study multiple technologically important systems, starting with carbon-nanotubes (CNT) and their interfaces in this paper, and silicon-based heterostructures in our follow-up paper. We find that when it comes to quantum transport through interesting, complex heterostructures, the Huckel bandstructure offers a fair and practical compromise between orthogonal tight-binding theories (OTB) with limited transferability between environments under large distortion, and density functional theories (DFT) that are computationally quite expensive for the same purpose.
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a self consistent transport model for molecular conduction based on Extended Huckel theory with full three dimensional electrostatics
Journal of Chemical Physics, 2005Co-Authors: Ferdows Zahid, Avik W Ghosh, Lutfe Siddiqui, Magnus Paulsson, Eric Polizzi, Supriyo DattaAbstract:We present a transport model for molecular conduction involving an Extended Huckel theoretical treatment of the molecular chemistry combined with a nonequilibrium Green’s function treatment of quantum transport. The self-consistent potential is approximated by CNDO (complete neglect of differential overlap) method and the electrostatic effects of metallic leads (bias and image charges) are included through a three-dimensional finite element method. This allows us to capture spatial details of the electrostatic potential profile, including effects of charging, screening, and complicated electrode configurations employing only a single adjustable parameter to locate the Fermi energy. As this model is based on semiempirical methods it is computationally inexpensive and flexible compared to ab initio models, yet at the same time it is able to capture salient qualitative features as well as several relevant quantitative details of transport. We apply our model to investigate recent experimental data on alkane dithiol molecules obtained in a nanopore setup. We also present a comparison study of single molecule transistors and identify electronic properties that control their performance.
Jorge I Cerda - One of the best experts on this subject based on the ideXlab platform.
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three dimensional Extended Huckel theory nonequilibrium green s function spin polarized transport model for fe mgo fe heterostructures
Journal of Applied Physics, 2011Co-Authors: Tehseen Z Raza, Jorge I Cerda, Hassan RazaAbstract:Although the theory of tunnel magnetoresistance (TMR) in Fe/MgO/Fe heterostructures is well known, there is a discrepancy between the values predicted by ab initio calculations with a band gap of 5.2 eV and the ones predicted by other methods, e.g., empirical tight-binding with a band gap of 7.6 eV. To our knowledge, no one has yet used the same theory to explore the reasons behind this discrepancy. In this work, we report a three-dimensional atomistic nonequilibrium Green’s function transport model with two set of transferable Extended Huckel theory parameters for MgO; one with the experimental band gap of 7.8 eV and the other with the local density approximation of the density functional theory band gap of 5.2 eV. To capture the symmetry filtering property of MgO, we parameterize using the k-resolved orbital projected density of states as the benchmark. We show that the band gap has a significant effect on the barrier width dependence and the bias dependence of the transport quantities. By using the exp...
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Extended Huckel theory for band structure chemistry and transport i carbon nanotubes
Journal of Applied Physics, 2006Co-Authors: Diego Kienle, Jorge I Cerda, Avik W GhoshAbstract:We describe a semiempirical atomic basis Extended Huckel theoretical (EHT) technique that can be used to calculate bulk band structure, surface density of states, electronic transmission, and interfacial chemistry of various materials within the same computational platform. We apply this method to study multiple technologically important systems, starting with carbon nanotubes and their interfaces and silicon-based heterostructures in our follow-up paper [D. Kienle et al., J. Appl. Phys. 100, 043715 (2006), following paper]. We find that when it comes to quantum transport through interesting, complex heterostructures including gas molecules adsorbed on nanotubes, the Huckel band structure offers a fair and practical compromise between orthogonal tight-binding theories with limited transferability between environments under large distortion and density functional theories that are computationally quite expensive for the same purpose.
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Extended Huckel theory for band structure chemistry and transport ii silicon
Journal of Applied Physics, 2006Co-Authors: Diego Kienle, Jorge I Cerda, Kirk H Bevan, Gengchiau Liang, Lutfe Siddiqui, Avik W GhoshAbstract:In this second paper, we develop transferable semiempirical Extended Huckel theoretical (EHT) parameters for the electronic structure of another technologically important material, namely, silicon. The EHT parameters are optimized to experimental target values of the band dispersion of bulk silicon. We quantitatively benchmark our parameters to bulk electronic properties such as band edge energies and locations, effective masses, and spin-orbit coupling parameters, competitive with a nearest-neighbor sp3d5s* orthogonal tight-binding model for silicon of T. Boykin et al. [Phys. Rev. B 69, 115201 (2004)] that has been widely used to model silicon-based devices (see, e.g., A. Rahman et al. [Jpn. J. Appl. Phys. Part I 44, 2187 (2005)] and J. Wang et al. [Appl. Phys. Lett. 86, 093113 (2005)]). The transferability of the parameters is checked for multiple physical and chemical configurations, specifically, two different reconstructed surfaces, Si(100)-(2×1) and Si(111)-(2×1). The robustness of the parameters to...
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Extended Huckel theory for bandstructure chemistry and transport ii silicon
arXiv: Materials Science, 2006Co-Authors: Diego Kienle, Jorge I Cerda, Kirk H Bevan, Gengchiau Liang, Lutfe Siddiqui, Avik W GhoshAbstract:In this second paper, we develop transferable semi-empirical parameters for the technologically important material, silicon, using Extended Huckel Theory (EHT) to calculate its electronic structure. The EHT-parameters areoptimized to experimental target values of the band dispersion of bulk-silicon. We obtain a very good quantitative match to the bandstructure characteristics such as bandedges and effective masses, which are competitive with the values obtained within an $sp^3 d^5 s^*$ orthogonal-tight binding model for silicon. The transferability of the parameters is investigated applying them to different physical and chemical environments by calculating the bandstructure of two reconstructed surfaces with different orientations: Si(100) (2x1) and Si(111) (2x1). The reproduced $\pi$- and $\pi^*$-surface bands agree in part quantitatively with DFT-GW calculations and PES/IPES experiments demonstrating their robustness to environmental changes. We further apply the silicon parameters to describe the 1D band dispersion of a unrelaxed rectangular silicon nanowire (SiNW) and demonstrate the EHT-approach of surface passivation using hydrogen. Our EHT-parameters thus provide a quantitative model of bulk-silicon and silicon-based materials such as contacts and surfaces, which are essential ingredients towards a quantitative quantum transport simulation through silicon-based heterostructures.
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Extended Huckel theory for bandstructure chemistry and transport i carbon nanotubes
arXiv: Materials Science, 2006Co-Authors: Diego Kienle, Jorge I Cerda, Avik W GhoshAbstract:We describe a semi-empirical atomic basis Extended H\"uckel Theoretical (EHT) technique that can be used to calculate bulk bandstructure, surface density of states, electronic transmission and interfacial chemistry of various materials within the same computational platform. We apply this method to study multiple technologically important systems, starting with carbon-nanotubes (CNT) and their interfaces in this paper, and silicon-based heterostructures in our follow-up paper. We find that when it comes to quantum transport through interesting, complex heterostructures, the Huckel bandstructure offers a fair and practical compromise between orthogonal tight-binding theories (OTB) with limited transferability between environments under large distortion, and density functional theories (DFT) that are computationally quite expensive for the same purpose.
Helmut W Schmalle - One of the best experts on this subject based on the ideXlab platform.
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synthesis crystal structure high resolution optical spectroscopy and Extended Huckel calculations on cyclometalated re co 4 ppy ppy 2 phenylpyridine
Journal of Physical Chemistry A, 1997Co-Authors: Frederik W M Vanhelmont, Geoffrey F Strouse, Hans U Gudel, Claudia A Stuckl, Helmut W SchmalleAbstract:The cyclometalated complex [Re(CO)4(ppy)], where ppy- = 2-phenylpyridine, was synthesized. Its crystal and molecular structure was determined by X-ray diffraction. The lowest energy electronic excitations were studied by high-resolution optical spectroscopy at cryogenic temperature. The first excited state in [Re(CO)4(ppy)] is nominally a triplet ligand-centered state, with 1.8% metal-to-ligand charge transfer character mixed in through spin−orbit coupling. This induces a shortened lifetime (89 μs at 10 K) and the occurrence of metal−ligand vibrations in both absorption and luminescence spectra. The transition moment of the first electronic excitation lies in the molecular plane with a tilt toward the pyridine part of the ppy- ligand. This is derived from the polarized absorption measurements and confirmed by an Extended Huckel calculation. Splittings in the IR absorption bands are resulting from the presence of two crystallographically equivalent complexes in the unit cell which are tilted with respect t...
