[CP2K-user] SCF convergence issues

Marcella Iannuzzi marci... at gmail.com
Thu Nov 5 16:08:43 UTC 2020

Dear Evgenia Elizarova

Is this question related to the previous posts in this conversation? 
If yes, what I meant is to remove all the MM part and just carry out a DFT 
calculation of the QM part. 

On Thursday, November 5, 2020 at 3:29:42 PM UTC+1 zh... at gmail.com wrote:

> Dear  Marcella Iannuzzi
> I've just started to explore opportunities of the cp2k package. I've done 
> some tutorials about single-point calculations of ethane molecule, QM/MM 
> simulations, and some more. I am very interested in single point energy 
> calculation for the QM part of the system. As I understood, I have to 
> define the force_eval section (method - quickstep), and also I have to 
> define subsections: dft, subsys, qmmm. Did I understand correctly? Also, i 
> have some questions.
> Do I have to define the MM subsection? In subsys section, I should define 
> the whole system?  How to define for which part of the system run a single 
> point calculation?
>  Could you help me, please?
> Best wishes, 
> Evgenia Elizarova
> понедельник, 2 ноября 2020 г. в 11:55:28 UTC+3, 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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