  We present a novel approach of mapping dissipative particle dynamics (DPD)
into classical molecular dynamics. By introducing the invariant volume element
representing the swarm of atoms we show that the interactions between the
emerging Brownian quasiparticles arise naturally from its geometric definition
and include both conservative repulsion and dissipative drag forces. The
quasiparticles, which are composed of atomistic host solvent rather than being
simply immersed in it, provide a link between the atomistic and DPD levels and
a practical route to extract the DPD parameters as direct statistical averages
over the atomistic host system. The method thus provides the molecular
foundations for the mesoscopic DPD. It is illustrated on the example of simple
monatomic supercritical fluid demonstrating good agreement in thermodynamic and
transport properties calculated for the atomistic system and DPD using the
obtained parameters.
