  Accurate equations of state (EOS) and plasma transport properties are
essential for numerical simulations of warm dense matter encountered in many
high-energy-density situations. Molecular dynamics (MD) is a simulation method
that generates EOS and transport data using an externally provided potential to
dynamically evolve the particles without further reference to the electrons. To
minimize computational cost, pair potentials needed in MD may be obtained from
the neutral-pseudoatom (NPA) approach, a form of single-ion density functional
theory (DFT), where many-ion effects are included via ion-ion correlation
functionals. Standard $N$-ion DFT-MD provides pair potentials via the force
matching technique but at much greater computational cost. Here we propose a
simple analytic model for pair potentials with physically meaningful parameters
based on a Yukawa form with a thermally damped Friedel tail (YFT) applicable to
systems containing free electrons. The YFT model accurately fits NPA pair
potentials or the non-parametric force-matched potentials from $N$-ion DFT-MD,
showing excellent agreement for a wide range of conditions. The YFT form
provides accurate extrapolations of the NPA or force-matched potentials for
small and large particle separations within a physical model. Our method can be
adopted to treat plasma mixtures, allowing for large-scale simulations of
multi-species warm dense matter.
