[CPMD-list] (no subject)

[Dr.Mehmet Cakmak]

No. I have still the same problem. 
Any other ideas.

If you are carrefully check my input file, you 
can easly see that I have made the bulk like 
calculations,i.e, fcc lattice with two basis atosms 
are fixed in their bulk like positions with using different 
lattice parameters and then I was tring to calculate
the energies. 

thank you

Mehmet Cakmak


> Hi 
> 
> I assume the problem is related to the small cell you are
> using. Certainly, the points raised by the others are
> also important, but I think that your problem is directly
> related to a NOT converged real space Ewald sum.
> The default in CPMD is to sum up the real space
> contributions of the Ewald sum only within the
> original supercell. If your cell is too small and you
> change the cell size you will see contributions
> of this. Check this assumption by running the
> simulations with 
> 
> TESR
> 4
> 
> Of course to get "good" results with small cells
> you should also have converged the cutoff (especially
> if you change the cell size) and k-points are important
> also. In addition I advice everybody to use more
> than the default value for the spline interpolation 
> points for the pseudopotentials.
> 
> SPLINE POINTS
> 3000
> 
> is a good start.
> 
> Juerg
> 
> ----------------------------------------------------------
> Juerg Hutter                   Phone :   41 1 635 4491
> Physical Chemistry Institute   FAX   :   41 1 635 6838
> University of Zurich           E-mail: hutter at pci.unizh.ch
> Winterthurerstrasse 190
> CH-8057 Zurich, Switzerland
> ----------------------------------------------------------
> 
> 
> On Wed, 7 Aug 2002, Dr.Mehmet Cakmak wrote:
> 
> > Dear All,
> > 
> > I am a bit puzzle to calculate lattice parameter of Si.
> > Please see the below table. When I take bigger lattice
> > parameter, the energy is getting smaller and smaller. 
> > There should be turning point which is going to be 
> > theoretical lattice parameter of Si. So any idea what could
> > be the reason? or do i know something wrong?
> > 
> >  E_tot       a_lat
> > -------      -----
> > -7.14         5.0      
> > -7.31         5.1
> > -7.36         5.2
> > -7.39         5.3
> > -7.43         5.4
> > -7.72         5.41    
> > -7.73         5.42
> > -7.74         5.43
> > -7.74         5.44
> > -7.75         5.45
> > -7.78         5.5
> > -7.83         5.6
> > -7.87         5.7
> > 
> > 	-mehmet
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> > 
>