[gmx-users] (dH/dl) calculation

[Mauricio Sica]

Dear experts

I am doing FEP (thermodynamic integration method) simulations.
I have a questions about <dH/dl> calculation in GROMACS.
Take in mind equation 3.77 from the GROMACS 3.3 manual.
There, dA/dl is calculated as

dA/dl = SS{ (dH/dl) exp()dp dq } / SS{ exp()dp dq = <dA/dl>NVT;l }

where SS are doble integrals (sorry for the notation).

My question is: how is (dH/dl) (in the middel-term of the equation) 
calculated?
My idea is that the difference V(L=1)-V(L=0) is calculated for every time 
step (irrespective of the lambda value of the simulation) and <dG/dl> is 
the time average of that difference. 

<dG/dl> = < V(L=1)(i)-V(L=0)(i)/1 >

Is this correct?


Thanks