[gmx-users] Energy drift

[Xiaobin Cao]

Thank you, Mark. Belows are what I found:

1, I test the double precision version. There is no drift with NVE, while the single one has.
2, Howerver, the bond energy drift still exists with NVT. I don't know why. 
3, For NVE simulation, the temperature is lower than what I generate. For example, the average temperature is aroud 273K if I generate the temperature at 298.15K. 
4, the diffusion coefficient calculated by NVE with 1 fs time step is ten times smaller than the experimental result at 298.15K, but the result is improved with 0.5 fs time step. 
5, I prefer to use NVT, because I can control the temperature. However, if the bond energy still drifts to high overtime, this will reduce rotation and translation energy because the kinetic energy and temperature are stable. If so, the calculated diffusion coefficient will be reduced, and this is consistent with my calculated results. Do yo have any idea to fix the bond energy drift in NVT ensemble?

By the way, my studied system is gas phase, which has a longer correlation time (about 2 ns). 

Thank you.
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>Hi,

>Repeating: how small a step is small enough to suppress the drift?

>Mark


_____________________________________________
Xiaobin Cao
Dept of Geology & Geophysics
E235, Howe-Russell Geosciences Complex,
Louisiana State University, Baton Rouge, LA 70803, U.S.A.