  We employ a novel multi-configurational self-consistent Green's function
approach (MCSCG) for the simulation of nanoscale Schottky-barrier field-effect
transistors. This approach allows to calculate the electronic transport with a
seamless transition from the single-electron regime to room temperature
field-effect transistor operation. The particular improvement of the MCSCG
stems from a division of the channel system into a small subsystem of
resonantly trapped states for which a many-body Fock space becomes feasible and
a strongly coupled rest which can be treated adequately on a conventional
mean-field level. The Fock space description allows for the calculation of
few-electron Coulomb charging effects beyond mean-field.
  We compare a conventional Hartree non-equilibrium Green's function
calculation with the results of the MCSCG approach. Using the MCSCG method
Coulomb blockade effects are demonstrated at low temperatures while under
strong nonequilibrium and room temperature conditions the Hartree approximation
is retained.
