The processes of radiation damage, from initial defect production to m
icrostructure evolution, occur over a wide spectrum of time and size s
cales. An understanding of the fundamental aspects of these processes
requires a spectrum of theoretical models, each applicable in its own
time and distance scales. As elements of this multimodel approach, mol
ecular dynamics and binary collision simulations play complementary ro
les in the characterization of the primary damage state of high energy
collision cascades. Molecular dynamics is needed to describe the indi
vidual point defects in the primary damage state with the requisite ph
ysical reality. The binary collision approximation is needed to model
the gross structure of statistically significant numbers of high energ
y cascades. Information provided by both models is needed for connecti
ng the defect production in the primary damage state with the appropri
ate models of defect diffusion and interaction describing the microstr
ucture evolution. Results of binary collision simulations of high ener
gy cascade morphology are reviewed. The energy dependence of freely mi
grating defect fractions calculated in recent molecular dynamics simul
ations are compared to results obtained much earlier with a binary col
lision/annealing simulation approach. The favorable agreement demonstr
ates the viability of the multi-model approach to defect production in
high energy cascades.