[CP2K-user] [CP2K:21766] Re: Single point energy diverges in large box, but converges in smaller box? P_Mix problem?

[Marcella Iannuzzi]

Hi Andreas, 

This is a structure problem. Having a triclinic cell with c vector  1.625   
  1.123    10.481 
you cannot expect to add something to the z component and maintain the same 
symmetry. 
The angles alpha and beta are change and probably the box is not anymore consistent 
with the coordinates.
Regards
Marcella

CELL_TOP| Vector a [angstrom    37.453     0.000     0.000   |a| =    
37.452754

 CELL_TOP| Vector b [angstrom   -20.749    29.823     0.000   |b| =    
36.331227

 CELL_TOP| Vector c [angstrom     1.625     1.123    10.481   |c| =    
10.665429

 CELL_TOP| Angle (b,c), alpha [degree]:                                
90.034600

 CELL_TOP| Angle (a,c), beta  [degree]:                                
81.235440

 CELL_TOP| Angle (a,b), gamma [degree]:                               
124.828009



CELL_TOP| Vector a [angstrom    37.453     0.000     0.000   |a| =    
37.452754

 CELL_TOP| Vector b [angstrom   -20.749    29.823     0.000   |b| =    
36.331227

 CELL_TOP| Vector c [angstrom     1.625     1.123    16.481   |c| =    
16.598865

 CELL_TOP| Angle (b,c), alpha [degree]:                                
90.022232

 CELL_TOP| Angle (a,c), beta  [degree]:                                
84.381360

 CELL_TOP| Angle (a,b), gamma [degree]:                               
124.828009

On Friday, August 22, 2025 at 2:53:43 PM UTC+2 andreas... at gmail.com wrote:

> Hallo,
>
> I want to calculate RESP charges for a COF structure with pbc in x and y 
> direction. For ease I put vacuum on top to get the charges of a singular 
> layer. This procedure worked out for another structure with 66 atoms. 
>
> For this structure which has 132 atoms, the single point energy 
> calculation FAILS! The energy quickly diverges if I consider a large box in 
> z direction, but converges if I have a smaller box. What is the reason for 
> that? At the P_Mix step it diverges, I cannot even get to DIIS minimizer!
>
> I have attached the input file resp.inp, the only thing changed between 
> runs is the cell in z direction from 16 A to 10 A as well as the xyz 
> structure and the output for the large cell. The working output.dat is also 
> attached. Note again that the only thing which I changed is the smaller 
> cell.
>
> Any input is appreciated, as I do not understand why the cell size makes 
> the energy diverge!
>
> Sincerely, 
> Andreas Doell
>

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