[gmx-users] timestep

[David van der Spoel]

On Mon, 25 Mar 2002, David L. Bostick wrote:

>
>Hello,
>
>I have gotten the same thing before when changing from 2fs timesteps to
>.1fs timesteps for 1 ps and then back to 2fs timesteps.  Everything went
>nuts.. the pressure, box size, and temperature increased.  It took about
>300 ps for the system to recover after switching back to 2 fs.  

Maybe one needs double precisiopn for that, since the shake contribution 
to the virial is computed by dividing the displacement by dt^2, so that's 
a factor of 400 on the virial. Any noise, on the already noisy virial will 
be enhanced considerably.

Groeten, David.
________________________________________________________________________
Dr. David van der Spoel, 	Biomedical center, Dept. of Biochemistry
Husargatan 3, Box 576,  	75123 Uppsala, Sweden
phone:	46 18 471 4205		fax: 46 18 511 755
spoel at xray.bmc.uu.se	spoel at gromacs.org   http://zorn.bmc.uu.se/~spoel
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