On Wed, Jul 31, 2013 at 7:47 PM, Janne Hirvi <janne.hi...@uef.fi> wrote: > Dear gmx-users, > > I have run some tests (especially) for pure water, being able to achieve > pretty much perfect energy conservation in > NVE ensemble (with PME-switch and shifted VDW potential).
Great. > Then, just for the test, I continued to NVT ensemble by using previous .tpr > and .cpt files, but the result was a quite > surprise, because there seems to be constant drift in "Conserved En.". > > The drift (100kJ/mol = 0.3%) is not especially large, but it exists with > v-rescale temperature coupling. On the other > hand, there is no drift at all, if I change to nose-hoover temperature > coupling. > > The behavior is similar also my other systems (liquid mixtures), even though > then neither of temperature coupling > methods will give exactly perfect conservation, but nose-hoover gives much > better one (500 kJ/mol = 3% vs. 60 > kJ/mol = 0.4%). > > Actually, I was expecting to see no drift at all, after all systems behaved > fine in NVE ensemble with same parameters > with an exception of added temperature coupling (especially when I used > double precision for test purpose). > > So, the main question is, if it is just normal that even such parameters, > which give perfect energy conservation in NVE > ensemble may introduce drift in "Conserved En.", when NVT ensemble is used? > Or is it just purely (only reason for drift) > indication that some temperature coupling methods"work better" than others in > this sense? In the case of v-rescale, the description of "Conserved En." is an overbid. If you see the Bussi 2007 paper, there is a conserved quantity H-tilde, but computing it requires knowledge of the whole of history. IIRC their H is what mdrun reports as "Conserved En.". I don't know whether it can be shown that a linear trend in H is equivalent to conservation in H-tilde, but that would be a useful result! Mark -- gmx-users mailing list gmx-users@gromacs.org http://lists.gromacs.org/mailman/listinfo/gmx-users * Please search the archive at http://www.gromacs.org/Support/Mailing_Lists/Search before posting! * Please don't post (un)subscribe requests to the list. Use the www interface or send it to gmx-users-requ...@gromacs.org. * Can't post? Read http://www.gromacs.org/Support/Mailing_Lists
