Questions about a system of molecules

Conrad cjohns... at
Sun Aug 14 11:39:31 UTC 2016

Hi Gary,

On Thursday, August 11, 2016 at 7:58:08 PM UTC+1, Gary wrote:
> Hi,
> I am trying to calculate the electric field above a system of molecules. 
> The molecules are arranged on the xy plane. I have done the same for single 
> molecule case, and that is working fine.
> My question is, how should I optimise the geometry? If it's a system of 
> molecules, I want to retain the configuration, but relax the system? There 
> are 4 molecules, and each molecule has 50 atoms, so there are a total of 
> 200 atoms. Is this too many for geometry optimisation? 

By retaining the configuration, do you mean the symmetry? 
Is it too many? No. CP2K scales to thousands of atoms. As a first 
approximation of computer time, budget for a few hundred self-consistent 
energy calculations' worth. 

I did a calculation of the EFIELD_CUBE without optimisation, and the 
> results are a little strange. The field is asymmetrical and seems to 
> completely concentrate around one of the 4 molecules. The magnitudei of the 
> field is also very high. I have attached the input and output files. There 
> is a total charge of -1. 

Have a look at the SPIN DENSITY cube. What you're doing in this input is 
effectively introducing an excess electron by having a non-zero overall 
charge. The SPIN DENSITY cube will show you where the unpaired charge 
(de)localises and may give you some clues. I've never spent any time 
looking at EFIELD data so I can't comment on this directly. 

> I also want to point out that the SCF run does not converge in the inner 
> loop (MAX_SCF 800); I am not sure if this is causing non-sensical data.
This is okay. You might even want to reduce MAX_SCF for the inner loop. 
When using OT, preconditioning is repeated before running over the inner 
loop. In principle, shorter inner loops can improve convergence. 

Anyway, this calculation is converged, so no issue there.

> Thanks,
> Gary

Finally, I notice that you're using version 2.2 of the code. This is really 
old, and may have some legacy bugs that haven't been patched.

Best wishes,
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