MTTK conserved energy is drifting
When I used MTTK integrator, the conserved energy (not total energy) of MTTK is drifting during the simulation.
It is drifting with a constant ratio of ca. -185 kJ/mol/ps.
The drift is caused even when I use the double precision version, and switching potential, and 0.5 fs time-step.
Although the fluctuation in the conserved energy is possible by nature of MTTK equation, constant drift during the full simulation time is not what I expect.
The problem is reproduced with either gcc 4.6.1 or icc 11.1.
grompp_d -f mpt-mttk05.mdp -c conf.gro -p spce.top -o mttk
mdrun_d -deffnm mttk
Fix for the pressure in MTTK with constraints + dispersion
Fix for pressure in MTTK - broken at some point in the
merge process. The MTTK+constraints code definitely needs to
be simplified for 5.0, it's too easy to break on code rearrangements
Testing with simple systems over long time shows that the pressure is
unbiased, while the PR pressure is off by a factor of 1/N (which is totally
fine for most realistic systems).
Fixes redmine bug #1061
#1 Updated by Michael Shirts about 6 years ago
- % Done changed from 0 to 100
OK, the commit submitted to 4.6 appears to fix this:
You can check it out -- in a run out to 16 ps. the conserved quantity has stayed within 10 kJ/mol from the total energy, as it should, and is not drifting up -- in the .xvg above, it had dropped 2000 kJ/mol by this point in the code.
When 4.6 is out, I'll go back and figure out the proper changes to backport to 4.5-patches.