  In numerous realizations of complex plasmas, dust-dust interactions are
characterized by two screening lengths and are thus better described by a
combination of Yukawa potentials. The present work investigates the static
correlations and the thermodynamics of repulsive dense bi-Yukawa fluids based
on the fact that such strongly coupled systems exhibit isomorph invariance. The
strong virial-potential energy correlations are demonstrated with the aid of
molecular dynamics simulations, an accurate analytical expression for the
isomorph family of curves is obtained and an empirical expression for the
fluid-solid phase-coexistence line is proposed. The isomorph-based empirically
modified hypernetted-chain approach, grounded on the ansatz of isomorph
invariant bridge functions, is then extended to such systems and the resulting
structural properties show an excellent agreement with the results of computer
simulations. A simple and accurate closed-form expression is obtained for the
excess internal energy of dense bi-Yukawa fluids by capitalizing on the compact
parameterization offered by the Rosenfeld-Tarazona decomposition in combination
with the Rosenfeld scaling, which opens up the energy route to thermodynamics.
