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

[David van der Spoel]

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
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++