[gmx-users] Computing work from pulling simulations

[Lutz Maibaum]

I am using “umbrella pulling” to simulate the dissociation of two molecules. I would like to calculate the work W(t) that the harmonic trap has performed on my system up to timestep t, which can be calculated as

W(t) = sum_{i=0}^t F_i * v * dt

where F_i is the biasing force at timestep i, v is the pulling velocity, and dt is the timestep. The latter two I set in the .mdp file, and the force is written out by Gromacs to the  pull_pullf.xvg file. 

This works very well. However, computing the work using the equation above requires me to save the forces to a file _every single timestep_, which becomes unfeasible for longer simulations. Does Gromacs keep track of the cumulative work performed by the umbrella potential, and does it save that value somewhere? I couldn’t find it in the .edr or log files (I am using Gromacs 5.1.4). 

Best,

Lutz