[gmx-users] Parameter file - dt and nsteps

[Fernando Mattio]

Dear Gromacs users,
I want to perform simulations of 3 ns with gromacs, and I believe that the
simulation time is determined in the parameter file (dt and nsteps). I
performed simulation of 0,1 ns with dt=0,002 and nsteps =50000, and it was
ok after 100 minutes. So I am really worried about how much time a 3 ns
simulation can takes!
I realized that if I changed the dt it could go faster (with less time
steps), but every time I did it (dt = 0,004, dt = 0,02, dt = 0,004, dt = 2)
my system collapsed!
It consists of a protein in a box of water... And I read somewhere in the
gromacs forum that for a system (protein and solvent) like this I could use
at most dt = 2 femtoseconds.
So shouldn´t it work?
The Fatal error was always:

Number of grid cells is zero. Probably the system and box collapsed.

Any information or advices about would be nice because I am new user of
gromacs.
Or the only way is to be very very patient?

Thank you very much in advance,
Fernando Mattio
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