Hello Gromacs users, Recently I ran some test particle insertion simulations of TIP4P/2005 water to measure the chemical potential at 470 K and 0.861 g/cc. I found that the chemical potential was 20%-25% higher than literature values. I believe there may be a problem related to using PME with test-particle insertion.
To test the PME code, I ran a very short TPI run of a water configuration with one molecule deleted. I forced insertions into the hole by using "tpic" mode. I compared the potential energies of these insertions with those obtained by simply taking the difference in potential energy of two md runs, where one contains the missing molecule and one has a hole instead. I ran mdrun in with the "-debug 1" option and added a line of code to tpi.c to print out the insertion locations. I am running the "release-4-5-patches origin/release-4-5-patches branch" of Gromacs 4.5.1. The LJ and short-range coulomb energies agree well, but the long-range coulomb energy does not. Compare 0.0229272 kJ/mol in TPI mode with -8.771680 kJ/mol in MD mode. Note that the total energy changes are -61.19020 and -69.97481, respectively. Input files for these tests can be found at http://bugzilla.gromacs.org/show_bug.cgi?id=590 . -Kevin -- 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
