[gmx-developers] Which integrator/coupling for accurate fluctuations?

[hess at sbc.su.se]

Hi,

But you don't really know how accurate the force-field is, do you?
You should be checking the conserved energy quantity to see
if that is well conserved and does not fluctuate too much.
I think this is not calculated for LF NPT.
I think what you want is Michael Shirts' newly implemented
VV integrator with proper coupling, which I think is Nose-Hoover + MTTK.
This should give the best possible integration.
You should then also get the conserved quantity, so you can actually
check your integration.

Berk

> Hi,
>
> we are trying to get accurate fluctuation properties out of mdrun. For
> this purpose I have built in a calculation of the enthalpy (Etot + pV)
> and store that in the energy file for maximum accuracy.
>
> Which NPT algorithm/integrator combination is recommended that minimally
> disturbs the fluctuations?
> Initial tries with Leap Frog/Nose Hoover/Parrinello Rahman give us
> fluctuations that are quite a bit too large (using GAFF):
> methanol: cp_exp=81, cp_gaff=141
> ethanol:cp_exp=122, cp_gaff=211
>
> This is from equilibrated boxes with 512 molecules. Any hints,
> suggestions?
>
> --
> David.
> ________________________________________________________________________
> David van der Spoel, PhD, Professor of Biology
> Dept. of Cell and Molecular Biology, Uppsala University.
> Husargatan 3, Box 596,  	75124 Uppsala, Sweden
> phone:	46 18 471 4205		fax: 46 18 511 755
> spoel at xray.bmc.uu.se	spoel at gromacs.org   http://xray.bmc.uu.se/~spoel
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>
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