[gmx-users] Energy drift problem

[xzp02 at mails.tsinghua.edu.cn]

Dear All:
    I ran a simulation for 5ns, no cut-off for VDW interaction, but finally I
found my system(1200 atoms) have a total energy drift of 60kJ/mol! I think it's
quite large. How large is the tolenrance typically? and which parameter can cause
it?
    I have read some posts before, and found that nstlist and vdw switch/shift can
cause this, but I have a 1ps test, with no VDW cut-off, nstlist = 1and 10 give
exactly the same total energy, but VDW cut-off may take into some not very large
drift.
    In the output of g_energy, which is the unit of Drift, kJ/mol? and is there
some critical value for it?

--out put of g_energy------------------------------------------------------------
Energy                      Average       RMSD     Fluct.      Drift  Tot-Drift
-------------------------------------------------------------------------------
Potential                   6758.88    106.825    106.753  0.0067678    13.5356
Kinetic En.                 6493.01    105.552    105.504  0.0055092    11.0184
Total Energy                13251.9    8.03478    3.78364   0.012277     24.554
Temperature                  407.05    6.61713    6.61412 0.000345374   0.690749
Heat Capacity Cv:      12.4767 J/mol K (factor = 0.000264268)
---------------------------------------------------------------------------------
    Thanks a lot.

ZP