[gmx-users] Problems of test particle insertion with gromacs 4.0

[Zhang Zhigang]

Hi all,
   I'm trying to use gromacs 4.0 to carried out some calculations with test
particle insertion algorithm.
   Here are my operations:
   0. Carried out a common NPT simulation with N molecules, I got the .trr
file;
   1. prepare .top and .gro with N+1 molecules (including the test
particle);
   2. use grompp to get the .tpr for mdrun;
   3. mdrun -rerun .trr.
   In this way, I finally got two files tpi.xvg and tpidist.xvg. The
procedure seems fine, isn't it?
   Nevertheless, I have some problems here:
   1. when I was trying to use pme (or EWALD) for the electrostatics, the
grompp stopped with an error: "TPI does not work with full electrostatics".
But if I use cut-off, the grompp works but generates a warning to recommend
the use of pme or reaction field. What's wrong here?
   2. The final output of mu seems to be sensitive to the choice of nsteps
(I've tried from 1000 to 10000). How to choose an appropriate one?

Thanks for your possible suggestions!

zgzhang
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