[gmx-users] why files are so large?

[Albert]

Hello:

   I am using the following settings for output file:

dt              = 0.002         ; Time-step (ps)
nsteps          = 2500000000    ; Number of steps to run (0.002 * 500000 
= 1 ns)

; Parameters controlling output writing
nstxout         = 5000000               ; Write coordinates to output 
.trr file every 2 ps
nstvout         = 5000000               ; Write velocities to output 
.trr file every 2 ps
nstfout         = 0
nstxtcout       = 50000
nstenergy       = 500000        ; Write energies to output .edr file 
every 2 ps
nstlog          = 500000        ; Write output to .log file every 2 ps


and I obtained following warnings from grompp:

NOTE 2 [file md.mdp]:
   This run will generate roughly 2791985478365075968 Mb of data


however, when I set
nstxout=0
nstvout=0
nstoout=0

I obtained following informations:

This run will generate roughly -9066 Mb of data

why it file size is negative? Moreover, my nstxout is very large, I 
don't know why the file is so big and no matter how did I change 
nstxout, nstvout, the files size doesn't change at all. it always claimed:


   This run will generate roughly 2791985478365075968 Mb of data

thank you very much
Albert