  We consider a projection operator approach to the non-equilbrium Green
function equation-of-motion (PO-NEGF EOM) method. The technique resolves
problems of arbitrariness in truncation of an infinite chain of EOMs, and
prevents violation of symmetry relations resulting from the truncation. The
approach, originally developed by Tserkovnikov [Theor. Math. Phys. 118, 85
(1999)] for equilibrium systems, is reformulated to be applicable to
time-dependent non-equilibrium situations. We derive a canonical form of EOMs,
thus explicitly demonstrating a proper result for the non-equilibrium atomic
limit in junction problems. A simple practical scheme applicable to quantum
transport simulations is formulated. We perform numerical simulations within
simple models, and compare results of the approach to other techniques, and
(where available) also to exact results.
