Geometry Optimisation of Large Charged Systems

[Rolf David]

Hi Olivia & Marcella, 

I allow myself to jump back on this problem/answer, and ask the CP2K 
team/users:

For a MD calculation (or maybe other, geometry for example here), is there 
a way to stop it if the SCF hasn't converged (after the inner/outer SCF) ? 

I try to find in the manual but no infos (or i looked at the wrong place ?)

If one SCF didn't converge, forces are still calculated and MD goes on to 
next step. So I kill it manually, but making it automatically save CPU 
usage and tell you right away: "No convergence, please check".

Thanks

Best regards,

Rolf

On Thursday, July 16, 2015 at 1:59:54 PM UTC+2, Marcella Iannuzzi wrote:
>
>
>
> Dear Olivia,
>
> The SCF in your run is never converging. Forces  calculated from a not 
> converged SCF are affected by large errors,  which explains the behaviour 
> of the geometry optimisation. 
> One shouldn't  carry on a geometry optimisation run when the SCF does not 
> converge.
> Allowing a larger number of SCF iterations might help (see OUTER_SCF / 
> MAX_SCF).
>
> Kind regards
> Marcella 
>
> On Thursday, July 16, 2015 at 12:41:44 PM UTC+2, Olivia Lynes wrote:
>>
>> Hi all,
>>
>> I'm having a problem with a few of my geometry optimisations not 
>> converging after several thousand steps and having looked at the energy 
>> changes through the main output file it's not decreasing but is fluctuating 
>> a lot in a certain range. I'm at a loss to why as I've got similar 
>> calculations completed with similar input and just a different box size and 
>> they have converged without this fluctuation in a few hundred steps.
>>
>> I've attached the input, coordination files and the first hundred or so 
>> steps of the output file.
>>
>> These are geometry optimisations of an Mg 2+ ion in a box of 64 waters, 
>> with a cell size of 13.41 angstroms, so the overall system is charged 2. 
>> I've used the GTH DZVP basis sets and potentials. 
>>
>> Having done a cell optimisation on just the 64 waters, we introduced the 
>> Mg ion and charged the system. In lieu of being able to do cell 
>> optimisations on a charged system, then geometry optimisations are being 
>> done at varying box sizes by 10ths of an angstrom as a sort of manual cell 
>> optimisation to try to find both a minimum energy structure and a minimum 
>> energy box size. 
>>
>> I've done similar calculations using Ca and Sr and haven't had this issue 
>> with any of my jobs, they all converge in a few hundred steps. 
>>
>> Is this potentially a problem using charged systems? Is it necessary for 
>> me to put a counter ion in which would let me do a standard cell 
>> optimisation? 
>>
>> Or is this approach completely wrong and we would be better off doing MD? 
>>
>> The aim is to do ab initio MD on these systems to look at the 
>> coordination of the ion in a bulk of water, so reaching a minimum energy 
>> structure and box size isn't essential but it would be nice to have the 
>> regular DFT data to back it up. 
>>
>> Thanks in advance for any insights.
>>
>> Olivia
>>
>>
>>
>>
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