[gmx-developers] Conserved energy drifts horribly with md-vv

[David van der Spoel]

Hi,

as a continuation of our tests for getting good energy conservation etc. 
we compared the md and the md-vv integrators in single and double 
precision with the v-rescale thermostat. The md integrator does not 
conserve energy in sp but is find in dp with sufficiently short time 
steps (no constraints used anywhere). For md-vv the drift is horrible 
even in dp. Plotted is the drift in the conserved-energy term from the 
edr file. 1000 Molecules, 1 ns.

Dt(fs)  md/sp   md/dp   md-vv/sp  md-vv/dp
2       486     501      5350      5287
1       40      47       4915      4981
0.5     -30     18       4769      4938
0.25    -189    3        4306      4963
0.1     -996    5        2496      4956
0.05    -2783   4       -1464      4953

Clues?
-- 
David van der Spoel, Ph.D., Professor of Biology
Dept. of Cell & Molec. Biol., Uppsala University.
Box 596, 75124 Uppsala, Sweden. Phone:	+46184714205.
spoel at xray.bmc.uu.se    http://folding.bmc.uu.se