you are on the right way. set high pressure.
set cut-offs to half box side. run classical MD, ~10 000 steps, and, afterwards, manually increase the box sides to mimic the experimental density in the plane-wave DFT, run local optimization prior to AIMD. On Tue, Feb 16, 2016 at 4:01 PM, Miguel Caro <miguel.c...@aalto.fi> wrote: > Hello, > > I was wondering if there is any reason why one should expect a constant > pressure simulation not to work for a small cell. I am running a very small > cell (1.2 nm^3) simulation because I need it as input for ab initio MD. I > am trying to simulate NPT at 1 atm and it seems like my cell, a mixture of > water and methanol, is expanding uncontrollably (to 10 nm^3). > > Is it not possible to do NPT for cells this small? I should add that NVT > seems to work just fine for the same system. > > These are the settings I am using for the pressure coupling: > > Pcoupl = MTTK > tau_p = 0.2 > compressibility = 4.5e-5 > ref_p = 1.0 > > I have tried to do the same simulation with a supercell made up of 2x2x2 > periodic copies of my small cell and that seems to work fine. For that > simulation, the only difference besides the cell size was the neighbors > cutoffs, which I could increase from rlist = rcoulomb = 0.45, rvdw = 0.5 > for the small cell to rlist = rcoulomb = 0.8, rvdw = 1.1 for the supercell. > For the small cell the cutoff radii are rather limited by the box size. > > Thanks in advance, > Miguel > > -- > *Dr. Miguel Caro* > /Postdoctoral researcher/ > Department of Electrical Engineering and Automation, > and COMP Centre of Excellence in Computational Nanoscience > Aalto University, Finland > Personal email: *mcar...@gmail.com* > Work: *miguel.c...@aalto.fi* > Website: http://mcaroba.dyndns.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. > -- 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.
