The Non Equilibrium Green's Function (NEGF) method is a powerful
technique to compute quantum transport properties of nanoscale
electronic devices. It is applicable to a wide range of devices,
ranging from nano transistors, molecular switches, nano wires...
Accurately simulating such devices often requires a 2D or a full
3D model. This leads to a large computational expense. We review
existing methods for the fast computation of the density of charge
using the Schrodinger-Poisson equation, and propose a new
algorithm which has a significantly lower computational cost and
is exact (in the absence of computer roundoff errors). The
algorithm is applicable in the presence of various boundary
conditions for the source, drain and gate regions, and for devices
of arbitrary geometry.