2,830 research outputs found
Measuring excitation-energy transfer with a real-time time-dependent density functional theory approach
We investigate the time an electronic excitation travels in a supermolecular
setup using a measurement process in an open quantum-system framework. The
approach is based on the stochastic Schr\"odinger equation and uses a
Hamiltonian from time-dependent density functional theory (TDDFT). It treats
electronic-structure properties and intermolecular coupling on the level of
TDDFT, while it opens a route to the description of dissipation and relaxation
via a bath operator that couples to the dipole moment of the density. Within
our study, we find that in supermolecular setups small deviations of the
electronic structure from the perfectly resonant case have only minor influence
on the pathways of excitation-energy transfer, thus lead to similar transfer
times. Yet, sizable defects cause notable slowdown of the energy spread
A Pearson Effective Potential for Monte-Carlo simulation of quantum confinement effects in various MOSFET architectures
A Pearson Effective Potential model for including quantization effects in the
simulation of nanoscale nMOSFETs has been developed. This model, based on a
realistic description of the function representing the non zero-size of the
electron wave packet, has been used in a Monte-Carlo simulator for bulk, single
gate SOI and double-gate SOI devices. In the case of SOI capacitors, the
electron density has been computed for a large range of effective field
(between 0.1 MV/cm and 1 MV/cm) and for various silicon film thicknesses
(between 5 nm and 20 nm). A good agreement with the Schroedinger-Poisson
results is obtained both on the total inversion charge and on the electron
density profiles. The ability of an Effective Potential approach to accurately
reproduce electrostatic quantum confinement effects is clearly demonstrated.Comment: 13 pages, 11 figures, 3 table
Approximation of small-amplitude weakly coupled oscillators with discrete nonlinear Schrodinger equations
Small-amplitude weakly coupled oscillators of the Klein-Gordon lattices are
approximated by equations of the discrete nonlinear Schrodinger type. We show
how to justify this approximation by two methods, which have been very popular
in the recent literature. The first method relies on a priori energy estimates
and multi-scale decompositions. The second method is based on a resonant normal
form theorem. We show that although the two methods are different in the
implementation, they produce equivalent results as the end product. We also
discuss applications of the discrete nonlinear Schrodinger equation in the
context of existence and stability of breathers of the Klein--Gordon lattice
Accurate Complex Scaling of Three Dimensional Numerical Potentials
The complex scaling method, which consists in continuing spatial coordinates
into the complex plane, is a well-established method that allows to compute
resonant eigenfunctions of the time-independent Schroedinger operator. Whenever
it is desirable to apply the complex scaling to investigate resonances in
physical systems defined on numerical discrete grids, the most direct approach
relies on the application of a similarity transformation to the original,
unscaled Hamiltonian. We show that such an approach can be conveniently
implemented in the Daubechies wavelet basis set, featuring a very promising
level of generality, high accuracy, and no need for artificial convergence
parameters. Complex scaling of three dimensional numerical potentials can be
efficiently and accurately performed. By carrying out an illustrative resonant
state computation in the case of a one-dimensional model potential, we then
show that our wavelet-based approach may disclose new exciting opportunities in
the field of computational non-Hermitian quantum mechanics.Comment: 11 pages, 8 figure
Many-particle Hamiltonian for open systems with full Coulomb interaction: Application to classical and quantum time-dependent simulations of nanoscale electron devices
Premi a l'excel·lència investigadora. Àmbit de les Ciències Tecnològiques i Enginyeries. 2010A many-particle Hamiltonian for a set of particles with Coulomb interaction inside an open system is described without any perturbative or mean-field approximation. The boundary conditions of the Hamiltonian on the borders of the open system [in the real three-dimensional (3D) space representation] are discussed in detail to include the Coulomb interaction between particles inside and outside of the open system. The many-particle Hamiltonian provides the same electrostatic description obtained from the image-charge method, but it has the fundamental advantage that it can be directly implemented into realistic (classical or quantum) electron device simulators via a 3D Poisson solver. Classically, the solution of this many-particle Hamiltonian is obtained via a coupled system of Newton-type equations with a different electric field for each particle. The quantum-mechanical solution of this many-particle Hamiltonian is achieved using the quantum (Bohm) trajectory algorithm [X. Oriols, Phys. Rev. Lett. 98, 066803 (2007)]. The computational viability of the many-particle algorithms to build powerful nanoscale device simulators is explicitly demonstrated for a (classical) double-gate field-effect transistor and a (quantum) resonant tunneling diode. The numerical results are compared with those computed from time-dependent mean-field algorithms showing important quantitative differences
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