The energy drift will depend on details of the simulation (energy conservation is actually not a trivial topic). Using AMBER, for explicit solvent calculations using PME, I have typically seen fairly linear energy drifts between 1.E-07 (0.5fs time step, no SHAKE) and 1.E-05 (2.0fs time step, with SHAKE) in units of kT/ns/dof at 300K (dof = degree of freedom). This translates to something between 0.5 kcal/mol and 25 kcal/mol for 20ns for a system with 100k atoms. Some other codes report larger drifts (in kT/ns/dof) in the literature.
All the best,
Andy
On Dec 28, 2012, at 1:50 PM, Dr. Vitaly Chaban wrote:
> On Fri, Dec 28, 2012 at 10:06 PM, Ismail, Mohd F. <farid.ou.edu> wrote:
>
>> Hi, I want to ask the experience users, if anyone has seen where, during
>> equlibration with NPT, the energy converged, but when the simulation is
>> switched to NVE, the energy drifted, linearly, either increasing or
>> decreasing compare to the equilibration. Is this normal?
>>
>> The energy drift is linear, which makes me wonder why. If the system is
>> not fully equilibrated, I expect it to be random. The change in energy is
>> like 20kcal/mol for 20ns. Is this bad?
>>
>>
>
> Yes, it is bad. Probably, you have specified some bad (incompatible with
> NVE) parameters, which provoke energy leakage.
>
>
>
> --
> Dr. Vitaly V. Chaban
> MEMPHYS - Center for Biomembrane Physics
> Department of Physics, Chemistry and Pharmacy
> University of Southern Denmark
> Campusvej 55, 5230 Odense M, Denmark
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--
Dr. Andreas W. Goetz
Assistant Project Scientist
San Diego Supercomputer Center
Tel : +1-858-822-4771
Email: agoetz.sdsc.edu
Web : www.awgoetz.de
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Received on Fri Dec 28 2012 - 17:00:03 PST
