[gmx-users] FEP problem with lambda perturbation 1 to 0.95

Carsten Kutzner ckutzne at gwdg.de
Fri Aug 7 09:35:44 CEST 2009

On Aug 6, 2009, at 10:57 PM, Ragnarok sdf wrote:

> I am performing FEP do obtain the dimerization of a protein in
> membrane. The lambda intervals i am using are 0.05 for each window.
> After that I rerun each lambda .trr perturbing the system (plus)0.05
> and (minus)0.05 lambda value. Then with g-energy I obtain the deltaG
> for each delta lambda.
> Well, I have encountered a problem when trying to simulate the last
> window (1.0 - 0.95 ). The simulation runs for a while and then dies.
> The log file says
> Step 2200  Warning: Pressure scaling more than 1%.
Hi Fabricio,

do you use soft-core? If not, I think you need to, at least for
the intervals next to 0 and 1 to avoid singularities (these
can result in undefined / NaN forces). See chap. 4.5.1 and
7.3.23 in the manual.


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