Understanding the effects of low doses of ionizing radi ation on living systems requires detailed information on electron transport in biomaterials. This, in turn, can be obtained from the wave-vector- and frequency-depen dent dielectric response function of the system, ∈(q,ω), via the energy-loss function, Im[-1/∈( q,ω)]. We describe two different possible approaches to obtaining these functions, one based on the semiempirical tight-binding approximation, the other using Hedin's many-body treatment of quasiparticle states in solids. These methods are exemplified with calculations for cubic ice (as a model for cellular "structured" water) and trans- polyacetylene. The availability of supercomputers makes the application of these techniques feasible.
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