  Equilibration of polymer melts containing highly entangled long polymer
chains in confinement or with free surfaces is a challenge for computer
simulations. We approach this problem by first studying polymer melts based on
the soft-sphere coarse-grained model confined between two walls with periodic
boundary conditions in two directions parallel to the walls. Then we apply
backmapping to reinsert the microscopic details of the underlying bead-spring
model. Tuning the strength of the wall potential, the monomer density of
confined polymer melts in equilibrium is kept at the bulk density even near the
walls. In a weak confining regime, we observe the same conformational
properties of chains as in the bulk melt showing that our confined polymer
melts have reached their equilibrated state. Our methodology provides an
efficient way of equilibrating large polymer films with different thicknesses
and is not confined to a specific underlying microscopic model. Switching off
the wall potential in the direction perpendicular to the walls, enables to
study free-standing highly entangled polymer films or polymer films with one
supporting substrate.
