# NEB MEP convergence check

Hi,

I need some suggestions regarding Minimum energy path calculations using NEB implemented in LAMMPS. We will get some final conformation of each NEB replica after NEB calculations are over. Each replica must minimize its energy at each NEB step (except reparameterization). But how can we make sure the final set of conformations we obtain for each replica indeed represents conformations along the Minimum Energy Path?
I think one way could be to run the same simulation for longer minimization steps and see that the RMSD of each image is not changing much in the final steps. One other way is to make sure after some number of NEB steps, the energy of each replica should not decrease further.

Is there any other interesting way anyone can think of, to make sure we have converged to the correct MEP?

Thanks,
Srijan Singh

If by “longer min steps” you mean more iterations, then for the damped
dynamics minimizers (e.g. FIRE) which are used with NEB in LAMMPS,
that simply means set a lower tolerance. When a tolerance is reached
that also means your 2nd criterion is met, i.e. the energy (or forces
depending on how you set the tolerances) are decreasing by less than
that tolerance.

Steve

Hi Steve,

Also, will you be able to help me out a bit with this? : I am using verbose keyword to get supplementary output during my NEB simulation to better understand what is going on. I had a small confusion regarding how “angletangrad” is calculated. The documentation says:

“angletangrad” is the angle between the 3N-length tangent vector and the 3N-length force vector at image i.

I just wanted to make sure whether this 3N-length force vector also contains the contribution of nudging forces?

If that is the case, I was wondering if it would be possible to get the angle between the tangent vector and the “natural” force vector (ie. not including spring forces) for each atom in each replica? As far as my understanding goes, for each atom in each replica, if the natural force has zero perpendicular component to the tangent, then it satisfies the condition for the Minimum Energy Path. So, I could use this data to validate that I have indeed converged to the MEP.

Srijan Singh

Hi Steve,

Also, will you be able to help me out a bit with this? : I am using verbose keyword to get supplementary output during my NEB simulation to better understand what is going on. I had a small confusion regarding how “angletangrad” is calculated. The documentation says:

“angletangrad” is the angle between the 3N-length tangent vector and the 3N-length force vector at image i.

I just wanted to make sure whether this 3N-length force vector also contains the contribution of nudging forces?

If that is the case, I was wondering if it would be possible to get the angle between the tangent vector and the “natural” force vector (ie. not including spring forces) for each atom in each replica? As far as my understanding goes, for each atom in each replica, if the natural force has zero perpendicular component to the tangent, then it satisfies the condition for the Minimum Energy Path. So, I could use this data to validate that I have indeed converged to the MEP.