Semiempirical Geometry Optimization calculation with periodic boundary condition

David Stelter base... at
Thu Nov 7 18:33:30 UTC 2013

Hi Bharat,

You can simply supply more SCF iterations to try to force a convergence to 
solve your SCF problem. By default, MAX_SCF is 50 iterations with an 
accuracy (EPS_SCF) of 1x10^-5. These parameters can simply be added to your 
input file under the SCF section. Hopefully, the SCF convergence will fix 
the geometry problems! I am unable to test this for you as did not provide 
coordinates in the input file for your system.


On Wednesday, November 6, 2013 11:13:26 AM UTC-5, bharat wrote:
> Hello Everyone,
> I am trying to perform geometry optimization calculation using 
> semiempirical methods AM1, PM3, RM1, and PM6 with periodic boundary 
> condition for bulk water (64 water molecules, initial structure is from M. 
> D. Ben et al. J. Phys. Chem. Lett. 4, 3753 (2013)) . It is found that SCF 
> is not converged and the structures are very bad. (O-H bond lengths 
> increased to 5-8 A and structure is not converged.) 
> Does anyone have experience using semiempirical methods for PBC 
> calculation? Please see the .xyz file using AM1 method.
> All suggestions are appreciated. 
> Thank you.
> Bharat Sharma
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