The electronic conductance of a molecule making contact to electrodes isdetermined by the coupling of discrete molecular states to the continuumelectrode density of states. Interactions between bound states and continua canbe modeled exactly by using the (energy-dependent) self-energy, orapproximately by using a complex potential. We discuss the relation between thetwo approaches and give a prescription for using the self-energy to constructan energy-independent, non-local, complex potential. We apply our scheme tostudying single-electron transmission in an atomic chain, obtaining excellentagreement with the exact result. Our approach allows us to treatelectron-reservoir couplings independent of single electron energies, allowingfor the definition of a one-body operator suitable for inclusion intocorrelated electron transport calculations.
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