[CP2K-user] [CP2K:20455] GFN1-XTB for QM/MM

[Emma Stevens]

Hi all,

I'm trying to perform QM/MM umbrella sampling on a small molecule system in 
water using semiempirical QM methods in cp2k and gromacs for MD. I keep 
running into SCF convergence issues due to bonds to hydrogen atoms breaking 
in my QM region and likely leaving the QM cell since semiempirical methods 
don't support a periodic QM region.

I've reduced my time step from 1fs to 0.5fs and have tried varying the size 
of my QM cell (even up to the full box size) and reducing the KAPPA value 
for my two RC constraints.

I've done simulations on the same system using DFT and was not seeing these 
issues, so it's possible I'm missing a keyword that's relevant when using 
semiempirical methods. My cp2k input file, gromacs mdp file, and plumed 
file are attached. I would really appreciate any suggestions!

Thank you,
Emma

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