Hello, I'm doing studies on edge passivation of Germanene Nanoribbons using a variety of elements. With Hydrogen Geometry optimization went smoothly, but I'm struggling to get a good result with Iodine as the passivating element. I'm using the same settings as I did for Hydrogen, that is:

- Rattle atoms prior to script generator

- In the New Calculator Block use: ATK-DFT, GGA-PBE Correlation, 75 Hartree density mesh cutoff, 1x21x21 k-points, Tight Tier 1 basis set (I have also tried double zeta polarized)

- In the geometry optimization block use: 0.01 Force Tolerance, 0.0005 Stress Tolerance, 200 steps, max step size of 0.5A, constrain cell in x direction

I have also tried adjusting the lattice parameters to increase size of unit cell prior to calculations and various force and stress tolerance values. I get different results, but all clearly incorrect. Any advice would be appreciated.

I've attached an image of the nanoribbon prior to rattling and optimization, and the post optimization result