  Diamond is used extensively as a component in high energy density
experiments, but existing equation of state (EOS) models do not capture its
observed response to dynamic loading. In particular, in contrast with first
principles theoretical EOS models, no solid-solid phase changes have been
detected, and no general-purpose EOS models match the measured ambient
isotherm. We have performed density functional theory (DFT) calculations of the
diamond phase to ~10TPa, well beyond its predicted range of thermodynamic
stability, and used these results as the basis of a Mie-Greuneisen EOS. We also
performed DFT calculations of the elastic moduli, and calibrated an algebraic
elasticity model for use in simulations. We then estimated the flow stress of
diamond by comparison with the stress-density relation measured experimentally
in ramp-loading experiments. The resulting constitutive model allows us to
place a constraint on the Taylor-Quinney factor (the fraction of plastic work
converted to heat) from the observation that diamond does not melt on ramp
compression.
