convergence problem of Ions in implicit water (SCCS)

[li bingxin]

Dear CP2K users,

I am trying to relax the Mg2+ solvated ions in the implicit water using the self-consistent continuum solvation (SCCS) model  implemented in the CP2K code. I have tested the parameters for water molecules inside the implicit water according to Oliviero's paper: https://aip.scitation.org/doi/10.1063/1.3676407, and found a slightly more negative solvation energy (-7.77 eV) comparing to the experiment data (-6.3 eV). I assume this error can be accepted and use the aforementioned parameters for the relaxation of ions in implicit water.

However, when I try to calculate the solvated Mg2+/Mg + 6H2O clusters (anions and neutral cluster), I found the SCF can hardly get converged in this case. I tried Broyden mixing method and direct linear mixing method with small mixing alpha (0.1). But this can not make the calculation get converged. I was wondering how can I get the SCF converged (for instance, tuning the values for rho_max/min in the SCCS model)?

I have attached the input file and could anyone have any experience or ideas on this issue help me?

I am looking forward to your reply.

[Marcella Iannuzzi]

Hi ...

I don't know the basis set that you are using for Mg, however the PW cutoff looks far too low and only 2 valence electron for Mg might be not optimal.

I doubt that the smearing would be useful for such a system, anyway it is in general applied with mixing in the reciprocal space.

Alpha 0.1 is not very small, you can easily need much smaller value.

Regards

Marcella

[li bingxin]

Hi Marcella,

Thanks a lot for your suggestions.  I will try to use a larger cutoff value for the auxiliary plane waves and a smaller mixing alpha.

Best,

Bingxin 

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