“…The density matrix is defined as (17) Its temporal evolution is given by the Liouville equation (18) where [ ] is the Poisson bracket and is the Liouville operator. Equation (18) can be written in the following form for device modeling (19) Based on Wigner's definition, the Wigner function is the Fourier transform of the one-particle density (matrix) operator (20) Alternatively, by performing the Wigner transformation for the Schrödinger equation, one arrives at the Liouville transport equation, which gives the time evolution of the Wigner function for device modeling (21) where the time derivative with subscript denotes a term due to scattering and is the potential. In a simple form, the device is assumed to obey the Liouville equation (22) where is the collision operator (23) and is the transition rate from to .…”