No, unfortunately not.

There are some efforts under way, though. You might have a look at Gerrit Groenhofs "Gromacs Sheets" which describes some of the commonly used data structures in Gromacs.

We are currently implementing an automated source documentation system (doxygen), which extracts information about data structures and comments about them from the source code.

Note that both these projects are not nearly finished, so comments are more than welcome, preferably through the Gromacs Developers Maillist (you need to join to post).