A new adaptive cell average spectral element method (SEM) is proposed to solve the time-dependent Wigner equation for transport in quantum devices. The proposed cell average SEM allows adaptive non-uniform meshes in phase spaces to reduce the high-dimensional computational cost of Wigner functions while preserving exactly the mass conservation for the numerical solutions. The key feature of the pro- posed method is an analytical relation between the cell averages of the Wigner function in the k-space (local electron density for finite range velocity) and the point values of the distribution, resulting in fast transforms between the local electron density and local fluxes of the discretized Wigner equation via the fast sine and cosine transforms. Numerical results with the proposed method are provided to demonstrate its high accuracy, conservation, convergence and a reduction of the cost using adaptive meshes.

Non-equilibrium Green’s function (NEGF) is a general method for modeling non-equilibrium quantum transport in open mesoscopic systems with many body scattering effects. In this paper, we present a unified treatment of quantum device boundaries in the framework of NEGF with both finite difference and finite element discretizations. Boundary treat- ments for both types of numerical methods, and the resulting self-energy R for the NEGF formulism, representing the dis- sipative effects of device contacts on the transport, are derived using auxiliary Green’s functions for the exterior of the quantum devices. Numerical results with both discretization schemes for an one-dimensional nano-device and a 29 nm double gated MOSFET are provided to demonstrate the accuracy and flexibility of the proposed boundary treatments.

In this paper, we propose a parallel Schwarz generalized eigen-oscillation spectral element method (GeSEM) for 2-D complex Helmholtz equations in high frequency wave scattering in dispersive inhomogeneous media. This method is based on the spectral expansion of complex generalized eigen-oscillations for the electromagnetic fields and the Schwarz non-overlapping domain decomposition iteration method. The GeSEM takes advantages of a special real orthogonality property of the complex eigen-oscillations and a new radiation interface condition for the system of equations for the spectral expansion coefficients. Numerical results validate the high resolution and the flexibility of the method for various materials.

This paper presents a further numerical study of the interaction dynamics for solitary waves in a nonlinear Dirac model with scalar self-interaction, the Soler model, by using a fourth order accurate Runge-Kutta discontinuous Galerkin method. The phase plane method is employed for the first time to analyze the interaction of Dirac solitary waves and reveals that the relative phase of those waves may vary with the interaction. In general, the interaction of Dirac solitary waves depends on the initial phase shift. If two equal solitary waves are in-phase or out-of-phase initially, so are they during the interaction; if the initial phase shift is far away from 0 and π, the relative phase begins to periodically evolve after a finite time. In the interaction of out-of-phase Dirac solitary waves, we can observe: (a) full repulsion in binary and ternary collisions, depending on the distance between initial waves; (b) repulsing first, attracting afterwards, and then collapse in binary and ternary collisions of initially resting two-humped waves; (c) one-overlap interaction and two-overlap interaction in ternary collisions of initially resting waves.

In this paper a new algorithm is presented for calculating the Green’s function of the Schrödinger equation in the presence of block layered potentials. Such Green’s functions have various and practical applications in quantum modelling of electron transport within nano-MOSFET transistors. The proposed method is based on expansions of the eigenfunctions of the subordinate Sturm–Liouville problems and a collocation matching procedure along possibly curved interfaces of the potential blocks. Accurate numerical results are provided to validate the proposed algorithm.

This paper extends Runge-Kutta discontinuous Galerkin (RKDG) methods to a nonlinear Dirac (NLD) model in relativistic quantum physics, and investigates interaction dynamics of corresponding solitary wave solutions. Weak inelastic interaction in ternary collisions is first observed by using high- order accurate schemes on finer meshes. A long-lived oscillating state is formed with an approximate constant frequency in collisions of two standing waves; another is with an increasing frequency in collisions of two moving solitons. We also prove three continuum conservation laws of the NLD model and an entropy inequality, i.e. the total charge non-increasing, of the semi-discrete RKDG methods, which are demonstrated by various numerical examples.

This paper presents a numerical study of the interaction dynamics for the solitary waves of a nonlinear Dirac field with scalar self-interaction by using a fourth order accurate Runge-Kutta discontinuous Galerkin (RKDG) method. Some new interaction phenomena are observed: (a) a new quasi-stable long-lived oscillating bound state from the binary collisions of a single-humped soliton and a two-humped soliton; (b) collapse in  binary and ternary collisions; (c) strongly inelastic interaction  in ternary collisions; and (d)  bound states with a short or long lifetime from  ternary collisions.