[gmx-developers] Brainstorming ideas for minimally painless incorporation of an MC barostat (later MC moves in general)

[Shirts, Michael R. (mrs5pt)]

Hi, all-

Especially for Berk, but other ideas are likely to be very useful as well.

This is also filed as http://redmine.gromacs.org/issues/1562, which will
likely be a better place to hold the conversation moving forward (but I
wanted to publicize it first).

As we eliminate the iterative constraint pressure control method, it will
be important to introduce a replacement in-theory-exact barostat for
systems with constraints, and as discussed, and MC barostat is the best
replacement.
For an MC barostat, this becomes specifically:

Every nstpcouple steps:
  1. Compute the energy (force may not be needed - will have to think
about combinations with MD)
  2. Modify the coordinates (optionally the velocities, depending on the
flavor of MC barostat)
     a. For a MC barostat, no communication between nodes is required, as
atoms are guaranteed stay on the same node -- everything only changes by
scaling
     b. For general MC moves (will likely be best to eventually make it
general) communication between notes might be required.
  3. Reevaluate the energy
  4. Accept/reject based on energy difference (may require some other
Jacobian terms). KEY PART: 'reject' reverts the system to state before the
proposal
  5. Continue

What will need to change in the way the forces are calculated for this to
be possible? What other changes?


~~~~~~~~~~~~
Michael Shirts
Assistant Professor
Department of Chemical Engineering
University of Virginia
michael.shirts at virginia.edu
(434)-243-1821