[CP2K-user] SCF convergence issues

[Marcella Iannuzzi]

Dear Ryan Rogers

There is apparently a problem with the conservation of the charge on the QM 
grid. 

Did you try to run a single point energy calculation for the QM part alone?
Kind regards
Marcella

On Thursday, October 29, 2020 at 7:11:42 PM UTC+1 r... at nyu.edu wrote:

> I might add that I have not been able to identify any obvious problems 
> with the configurations (e.g. overlapping or too close atoms, etc.) when I 
> encounter these errors. 
>
> On Monday, October 26, 2020 at 4:07:46 PM UTC-5 Ryan Rogers wrote:
>
>> Dear CP2K community, 
>>
>> I am having issues in DFT QM/MM force calculations on molecular crystals 
>> of paracetamol (acetaminophen). I am describing here the two problems I 
>> most often experience. I am currently unable to identify the cause or any 
>> pattern in the problems I encounter. The root of the problems could be 
>> something other than what I identify below; I am pointing out the 
>> problematic features in the output that are most obviously to me. All input 
>> and output files are included. 
>>
>> *1. Total energy falls into "hole" and never converges. 
>> (CP2K_problemTotalE_conf_0636.tar.gz)*
>> Personal experience tells me to expect a "Total energy" for these systems 
>> on the order of -2,000 (Hartree) and a "Hartree energy" on the order of 
>> +2,000 (Hartree).
>> In these jobs, I find an initial "Hartree energy" on the order of 
>> >-10,000 (Hartree), which appears to send the SCF wavefunction optimization 
>> down a path of non-convergence, in which the "Total energy" can easily 
>> become on the order of -100,000 (Hartree) before I kill the job.
>>
>> *2. Total charge density on grids grows too large. 
>> (CP2K_problemEGrids_conf_0623.tar.gz)*
>> In these jobs, the Total energy looks reasonable, and the Convergence 
>> looks promising in the few SCF cycles of steps. 
>> However, the total Change never drops below my threshold, and eventually 
>> the "Total charge density on r-space/g-space grids" becomes much too large.
>>
>> My configurations are extracted from MD trajectories, so the atoms have 
>> perturbations from their perfect crystal positions. One confusing 
>> observation is that very similar QM/MM configurations selected from other 
>> frames of the same trajectory often have no problems.
>> My configurations are constructed from a cluster of several molecules in 
>> the QM region with usually another layer usually 1-2 molecules thick making 
>> up the MM region. (In the attached sample images, the size of the stick 
>> molecules alludes to a larger/smaller basis set used, while the MM atoms 
>> are denoted as points.) Because I am not including integer numbers of unit 
>> cells, I am not using PBC. 
>>
>> Any advice about both/either problem will be greatly appreciated!
>>
>> Sincerely,
>> Ryan Rogers
>> r... at nyu.edu
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>
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