Hello, Thank you very much for your thoughtfull response. The structural properties seem to be represented correctly so I guess it should work. I know that drifts are something we must live with but since it appeared when changing the system to a tabulated potential+a group cutoff I was not sure if I was making some mistake.
Sergio El 01/09/2017 12:48, Mark Abraham escribió: > Hi, > > There's not easy answers to such questions. A practical implementation of > MD that can actually do most relevant kinds of science in relevant time > frames can't have bitwise conservation. Drift accumulates from multiple > aspects of the implementation, too, including the system size, and > constraint algorithm, which can dominate over the effects of missing > interactions over the lifetime of pair lists. See the discussion in the > GROMACS reference manual, e.g. figure 3.5. > > One proper question to ask is at what point your protocol correctly models > whatever relevant physical data exists that is relevant to what you want to > observe. Drift that is too large is likely to affect observables, but will > affect different ones differently. > > Mark > > On Fri, Sep 1, 2017 at 12:12 PM <serper...@alum.us.es> wrote: > >> Dear GROMACS Community, >> >> I am trying to do a simulation using a tabulated potential which forces >> me to use the group cut-off. I get a drift in the conserved quantity of >> -600KJ/mol/ns. My system consists of 1000 rigid TIP4P water molecules >> and a Na+ ion. I imagine that eventhough it will soon be deprecated the >> group cutoff scheme still works correctly. I have tryed to change the >> parameters without success and in any case the ones I use seem >> reasonable (in my experience using other programs). The rdfs of the >> system look normal so I ruled out topology problems. >> >> It seems that the problem is in the group cut-off since >> when I change the tabulated potential for a regular vdw the problem >> persists. I have followed the instructions of: >> >> http://www.gromacs.org/@api/deki/files/94/=gromacs_nb.pdf >> >> to implement the tabulated potentials. >> >> Is this the kind of energy drift acceptable? I have pasted a copy .mdp >> >> Thanks for your help, >> >> Sergio Perez-Conesa >> >> integrator = md >> dt = 0.001 >> nsteps = 100000 >> init-step = 0 >> cutoff-scheme = group >> nst-list = 1 >> verlet-buffer-tolerance = 0.0005 >> ns-type = grid >> rlist = 1.3 >> pbc = xyz >> coulombtype = PME-switch >> rcoulomb = 1. >> rcoulomb-switch = 0.95 >> pme-order = 4 >> fourierspacing = 0.1 >> ewald-rtol = 1.e-5 >> vdwtype = user >> rvdw = 1.0 >> DispCorr = No >> tcoupl = v-rescale >> tc-grps = System >> ;nsttcouple = 1 >> tau-t = ref-t = 300.0 >> constraints = all-angles >> constraint-algorithm = LINCS >> lincs_iter = 1 >> lincs_order = 4 >> energygrps = NA OW >> energygrp_table = NA OW >> comm-mode = linear >> -- >> Gromacs Users mailing list >> >> * Please search the archive at >> http://www.gromacs.org/Support/Mailing_Lists/GMX-Users_List before >> posting! >> >> * Can't post? Read http://www.gromacs.org/Support/Mailing_Lists >> >> * For (un)subscribe requests visit >> https://maillist.sys.kth.se/mailman/listinfo/gromacs.org_gmx-users or >> send a mail to gmx-users-requ...@gromacs.org. -- Gromacs Users mailing list * Please search the archive at http://www.gromacs.org/Support/Mailing_Lists/GMX-Users_List before posting! * Can't post? Read http://www.gromacs.org/Support/Mailing_Lists * For (un)subscribe requests visit https://maillist.sys.kth.se/mailman/listinfo/gromacs.org_gmx-users or send a mail to gmx-users-requ...@gromacs.org.