  We describe a method for computing transport coefficients from the direct
evaluation of large deviation function. This method is general, relying on only
equilibrium fluctuations, and is statistically efficient, employing trajectory
based importance sampling. Equilibrium fluctuations of molecular currents are
characterized by their large deviation functions, which is a scaled cumulant
generating function analogous to the free energy. A diffusion Monte Carlo
algorithm is used to evaluate the large deviation functions, from which
arbitrary transport coefficients are derivable. We find significant statistical
improvement over traditional Green-Kubo based calculations. The systematic and
statistical errors of this method are analyzed in the context of specific
transport coefficient calculations, including the shear viscosity, interfacial
friction coefficient, and thermal conductivity.
