arXiv subjects

Ali Faraj

Publications and source records attributed to Ali Faraj.

4 recordsLinked to original sources

arXiv2015

The Landau-Zener transition and the surface hopping method for the 2D Dirac equation for graphene

A Lagrangian surface hopping algorithm is implemented to study the two dimensional massless Dirac equation for Graphene with an electrostatic potential, in the semiclassical regime. In this problem, the crossing of the energy levels of the system at Dirac points requires a particular treatment in the algorithm in order to describe the quantum transition-- characterized by the Landau-Zener probability-- between different energy levels. We first derive the Landau-Zener probability for the underlying problem, then incorporate it into the surface hopping algorithm. We also show that different asymptotic models for this problem derived in [O. Morandi, F. Sch{\"u}rrer, J. Phys. A: Math. Theor. 44 (2011)] may give different transition probabilities. We conduct numerical experiments to compare the solutions to the Dirac equation, the surface hopping algorithm, and the asymptotic models of [O. Morandi, F. Sch{\"u}rrer, J. Phys. A: Math. Theor. 44 (2011)].

math.AP↗

arXiv2010

Adiabatic evolution of 1D shape resonances: an artificial interface conditions approach

Artificial interface conditions parametrized by a complex number $θ_{0}$ are introduced for 1D-Schrödinger operators. When this complex parameter equals the parameter $θ\in i\R$ of the complex deformation which unveils the shape resonances, the Hamiltonian becomes dissipative. This makes possible an adiabatic theory for the time evolution of resonant states for arbitrarily large time scales. The effect of the artificial interface conditions on the important stationary quantities involved in quantum transport models is also checked to be as small as wanted, in the polynomial scale $(h^N)_{N\in \N}$ as $h\to 0$, according to $θ_{0}$.

math.AP↗

arXiv2010

Asymptotic analysis of a Schrödinger-Poisson system with quantum wells and macroscopic nonlinearities in dimension 1

We consider the stationary one dimensional Schrödinger-Poisson system on a bounded interval with a background potential describing a quantum well. Using a partition function which forces the particles to remain in the quantum well, the limit $h\rightarrow0$ in the nonlinear system leads to a uniquely solved nonlinear problem with concentrated particle density. It allows to conclude about the convergence of the solution.

math.AP↗

arXiv2010

A double scale fast algorithm for the transient evolution of a resonant tunneling diode

The simulation of the time-dependent evolution of the resonant tunneling diode is done by a multiscale algorithm exploiting the existence of resonant states. After revisiting and improving the algorithm developed in [N. Ben Abdallah, O. Pinaud, J. Comp. Phys. 213 (2006) 288-310] for the stationary case, the time-dependent problem is dealt with. The wave function is decomposed into a non resonant part and a resonant one. The projection method to compute the resonant part leads to an accurate algorithm thanks to a suitable interpolation of the non resonant one. The simulation times are largely reduced.

math.AP↗