[gmx-developers] doing energy evaluations at alternate lambda values (i.e. for bennett acceptance ratio)

[Erik Lindahl]

Hi,

On Jan 4, 2007, at 10:19 AM, David van der Spoel wrote:

>
> I think Mark is right in that no harm will come of trying different  
> lambda values, however it is important to use the correct forces  
> for doing the dynamics, that is you want to stay at your fixed  
> lambda value for the dynamics.
>
> So how would you specify the different lambda values that you would  
> want to try?

That's quite straightforward. I'm just replacing lambda with an array  
of values, where the first is used for the dynamics and the rest only  
for energy evalulations.  I've then modified the nonbonded free  
energy loop to calculate enthalpy _differences_ relative to the first  
lambda value.

I do have to loop over the lambda values, but only in the free energy  
loop, and since that normally only accounts for 1-2% of runtime it's  
not a problem to do it every single step.

Cheers,

Erik