[gmx-users] timestep

David van der Spoel spoel at xray.bmc.uu.se
Mon Mar 25 19:03:06 CET 2002

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

>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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