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Search Results: 1 - 10 of 32735 matches for " Daniel Boese "
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Thermoelectric effects in Kondo correlated quantum dots
Daniel Boese,Rosario Fazio
Physics , 2001, DOI: 10.1209/epl/i2001-00559-8
Abstract: In this Letter we study thermoelectric effects in ultra small quantum dots. We study the behaviour of the thermopower, Peltier coefficient and thermal conductance both in the sequencial tunneling regime and in the regime where Kondo correlations develope. Both cases of linear response and non-equilibrium induced by strong temperature gradients are considered. The thermopower is a very sensitive tool to detect Kondo correlations. It changes sign both as a function of temperature and temperature gradient. We also discuss violations of the Wiedemann-Franz law.
A magnetic barrier in confined two-dimensional electron gases: Nanomagnetometers and magnetic switches
Michele Governale,Daniel Boese
Physics , 2000, DOI: 10.1063/1.1325396
Abstract: We investigate the conductance properties of a hybrid ferromagnet-semiconductor structure consisting of a confined two-dimensional electron gas and a transverse ferromagnetic strip on top. Within the framework of the Landauer-B\"uttiker model, we develop an alternative way to consider magnetic fields. Our method describes devices ranging from a recently realized nanomagnetometer down to quasi one-dimensional quantum wires. We provide a rigorous way to relate the measured resistance to the actual magnetization of the strip. Regarding the quasi one-dimensional wires we propose a new device application, a tunable magnetic switch.
Influence of nano-mechanical properties on single electron tunneling: A vibrating Single-Electron Transistor
Daniel Boese,Herbert Schoeller
Physics , 2000, DOI: 10.1209/epl/i2001-00367-8
Abstract: We describe single electron tunneling through molecular structures under the influence of nano-mechanical excitations. We develop a full quantum mechanical model, which includes charging effects and dissipation, and apply it to the vibrating C$_{60}$ single electron transistor experiment by Park {\em et al.} {[Nature {\bf 407}, 57 (2000)].} We find good agreement and argue vibrations to be essential to molecular electronic systems. We propose a mechanism to realize negative differential conductance using local bosonic excitations.
Development of Novel Density Functionals for Thermochemical Kinetics
A. Daniel Boese,Jan M. L. Martin
Physics , 2004, DOI: 10.1063/1.1774975
Abstract: A new density functional theory (DFT) exchange-correlation functional for the exploration of reaction mechanisms is proposed. This new functional, denoted BMK (Boese-Martin for Kinetics), has an accuracy in the 2 kcal/mol range for transition state barriers but, unlike previous attempts at such a functional, this improved accuracy does not come at the expense of equilibrium properties. This makes it a general-purpose functional whose domain of applicability has been extended to transition states, rather than a specialized functional for kinetics. The improvement in BMK rests on the inclusion of the kinetic energy density together with a large value of the exact exchange mixing coefficient. For this functional, the kinetic energy density appears to correct `back' the excess exact exchange mixing for ground-state properties, possibly simulating variable exchange.
Anharmonic force fields of perchloric acid, HClO$_4$, and perchloric anhydride, Cl$_2$O$_7$. An extreme case of inner polarization
A. Daniel Boese,Jan M. L. Martin
Physics , 2005, DOI: 10.1016/j.molstruc.2005.07.009
Abstract: DFT (density functional theory) anharmonic force fields with basis sets near the Kohn-Sham limit have been obtained for perchloric acid, HClO$_4$, and perchloric anhydride, Cl$_2$O$_7$. Calculated fundamental frequencies are in very good agreement with available experimental data. Some reassignments in the vibrational spectra of Cl$_2$O$_7$ are proposed based on our calculations. HClO$_4$ and Cl$_2$O$_7$ are particularly severe examples of the `inner polarization' phenomenon. The polarization consistent basis sets pc-1 and pc-2 (as well as their augmented counterparts) should be supplemented with two (preferably three) and one (preferably two) high-exponent $d$ functions, respectively, on second-row atoms. Complete anharmonic force fields are available as electronic supporting information.
Vibrational Spectra of the Azabenzenes Revisited: Anharmonic Force Fields
A. Daniel Boese,Jan M. L. Martin
Physics , 2003, DOI: 10.1021/jp0369589
Abstract: Anharmonic force fields and vibrational spectra of the azabenzene series (pyridine, pyridazine, pyrimidine, pyrazine, s-triazine, 1,2,3-triazine, 1,2,4-triazine and s-tetrazine) and benzene are obtained using density functional theory (DFT) with the B97-1 exchange-correlation functional and a triple-zeta plus double polarization (TZ2P) basis set. Overall, the fundamental frequencies computed by second-order rovibrational perturbation theory are in excellent agreement with experiment. The resolution of the presently calculated anharmonic spectra is such that they represent an extremely useful tool for the assignment and interpretation of the experimental spectra, especially where resonances are involved.
Interference and interaction effects in multi-level quantum dots
Daniel Boese,Walter Hofstetter,Herbert Schoeller
Physics , 2000, DOI: 10.1103/PhysRevB.64.125309
Abstract: Using renormalization group techniques, we study spectral and transport properties of a spinless interacting quantum dot consisting of two levels coupled to metallic reservoirs. For strong Coulomb repulsion $U$ and an applied Aharonov-Bohm phase $\phi$, we find a large direct tunnel splitting $|\Delta|\sim (\Gamma/\pi)|\cos(\phi/2)|\ln(U/\omega_c)$ between the levels of the order of the level broadening $\Gamma$. As a consequence we discover a many-body resonance in the spectral density that can be measured via the absorption power. Furthermore, for $\phi=\pi$, we show that the system can be tuned into an effective Anderson model with spin-dependent tunneling.
Resonances in a two-dimensional electron waveguide with a single delta-function scatterer
Daniel Boese,Markus Lischka,L. E. Reichl
Physics , 1999, DOI: 10.1103/PhysRevB.61.5632
Abstract: We study the conductance properties of a straight two-dimensional electron waveguide with an s-like scatterer modeled by a single delta-function potential with a finite number of modes. Even such a simple system exhibits interesting resonance phenomena. These resonances are explained in terms of quasi-bound states both by using a direct solution of the Schroedinger equation and by studying the Green's function of the system. Using the Green's function we calculate the survival probability as well as the power absorption and show the influence of the quasi-bound states on these two quantities.
Mesoscopic effects in tunneling between parallel quantum wires
Daniel Boese,Michele Governale,A. Rosch,U. Zuelicke
Physics , 2001, DOI: 10.1103/PhysRevB.64.085315
Abstract: We consider a phase-coherent system of two parallel quantum wires that are coupled via a tunneling barrier of finite length. The usual perturbative treatment of tunneling fails in this case, even in the diffusive limit, once the length L of the coupling region exceeds a characteristic length scale L_t set by tunneling. Exact solution of the scattering problem posed by the extended tunneling barrier allows us to compute tunneling conductances as a function of applied voltage and magnetic field. We take into account charging effects in the quantum wires due to applied voltages and find that these are important for 1D-to-1D tunneling transport.
Anharmonic force fields and thermodynamic functions using density functional theory
A. Daniel Boese,Wim Klopper,Jan M. L. Martin
Physics , 2004, DOI: 10.1080/00268970512331339369
Abstract: The very good performance of modern density functional theory for molecular geometries and harmonic vibrational frequencies has been well established. We investigate the performance of density functional theory (DFT) for quartic force fields, vibrational anharmonicity and rotation-vibration coupling constants, and thermodynamic functions beyond the RRHO (rigid rotor-harmonic oscillator) approximation of a number of small polyatomic molecules. Convergence in terms of basis set, integration grid and the numerical step size for determining the quartic force field by using central differences of analytical second derivatives has been investigated, as well as the performance of various exchange-correlation functionals. DFT is found to offer a cost-effective approach with manageable scalability for obtaining anharmonic molecular properties, and particularly as a source for anharmonic zero-point and thermal corrections for use in conjunction with benchmark {\it ab initio} thermochemistry methods.
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