We released a patch today with several new “chunk” commands.
Chunks are defined as collections of atoms (molecules, spatial bins,
atoms with the same coordination #, etc), which you can define
in a variety of ways via compute chunk/atom. You can then sum per-atom
values by chunk. So this will replace fix ave/spatial (at some point
in the future) as a more general and flexible way to compute system properties
based on subsets of atoms.
This doc page gives a summary:
http://lammps.sandia.gov/doc/Section_howto.html#howto_23
These are the new commands:
compute chunk/atom, fix ave/chunk
compute com/chunk
compute gyration/chunk
compute inertia/chunk
compute msd/chunk
compute property/chunk
compute temp/chunk
compute torque/chunk
compute vcm/chunk
Steve