Convergence for awh

User discussions
1

GROMACS version:2020
GROMACS modification: No

Hello,

I am running a multiple walker awh simulation on a 1-D reaction coordinate. Upon comparing the PMFs at different times the PMF is converged. I also checked that the coordinate distribution ≈ reference target distribution and the reference target distribution ≈ target distribution. The target distribution was chosen to be uniform. Based on these observations I considered the PMF to be converged. However, the simulation never exited the initial stage. There were several coverings but never exited the initial stage. Can we still have a reliable PMF if the convergence criteria is satisfied but never exited the initial stage of AWH?

2

The PMF is usually not reliable in the initial stage.
So either you simulation is too short and/or your reaction coordinate is problematic.

3

I am now wondering if it could be that you chose some AWH parameter sub-optimal such that your sampling is actually converged, but it is not detected. Could you post you AWH and pull parameters?

4

Yes,sure. Here are the AWH and pull parameters I used:

;AWH calculations
pull = yes
pull_ncoords = 1 ; only one reaction coordinate
pull_ngroups = 2 ; two groups defining one reaction coordinate
pull_group1_name = LIG
pull_group2_name = r1180
pull_coord1_geometry = direction ; simple distance increase

pull_coord1_dim = N N Y ; pull along z
pull_coord1_groups = 1 2 ; groups 1 and 2 define the reaction coordinate
pull_coord1_start = yes ; define initial COM distance > 0
pull_coord1_rate = 0 ; 0.0005 nm per ps = 0.5 nm per ns
pull_coord1_k = 0 ; kJ mol^-1 nm^-2
pull_coord1_vec = 0 0 1

pull-coord1-type = external-potential
pull-coord1-potential-provider = awh

awh = yes
awh-potential = convolved
awh-share-multisim = yes
awh1-share-group = 1
awh-nbias = 1
awh-nstout = 50000
awh1-ndim = 1
awh1-dim1-start = 0.4
awh1-dim1-end = 4.0
awh1-dim1-diffusion = 5e-5
awh1-dim1-force-constant = 12800
awh1-equilibrate-histogram = yes
awh1-error-init = 20