Forcite and Mesocite can analyze trajectories for the concentration profile in one direction, as well as calculate mass density in three dimensions, for each frame individually. Attached script averages the density field over all frames, thus obtaining a 3d analogue of the concentration profile.

The input consists of a trajectory document. A set may be defined to restrict the atoms being analyzed. The output is a structure document containing the average field. The field can be further processed in the usual way (isosurfaces, slices, etc).

As field access can be quite slow, the script is best run server-side.

Below is an application to polystyrene chain grafted on a gold surface. The analysis applies to the repeat unit at the end of the chain.

Input
Output