[gmx-developers] TI and PMe in GROMACS

hessb at mpip-mainz.mpg.de hessb at mpip-mainz.mpg.de
Tue Feb 15 19:10:43 CET 2005

Quoting Martin Lepsik <lepsik at uochb.cas.cz>:

> Dear Berk,
> sorry, my mistake, I was confused with your terminology.
> You really have had TI in GROMACS (under TI, I understand dA = integr of 
> (ens.avg of dH/dlambda) over lambda.
> With slow growth (as you call it in the manual), one usually means dA = 
> sum of (ens.avg of (Hamilt at lambda+1 - Hamilt at lambda)) Now, this is 
> clear...

No, slow growth is the integral of dH/dlambda from 0 to 1,
using only two points is not "slow".
I think that with TI one usually means the same as slow growth.

Anyhow, on the code level all this does not matter. The only
thing that matters is if the proper dH/dlambda is calculated.

I have committed PME free-energy code on 2004/11/1.
If you check out the version of that day it will work.
Also in CVS the Reaction-field free-energy has been fixed
by adding the reaction-field correction to the excluded atom pairs.
This is described in the CVS manual.
PME free-energy is trivial. One needs to properply average the
potential and the forces with the lambda=0 and lambda=1 charges
and the difference of the lamdba=1 and lambda=0 potential gives


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