[Pw_forum] HCP and FCC site energy difference on Cu 111

[Stefano de Gironcoli]

Dear Wong Kelvin,

  In general I would expect the FCC vs HCP site energy difference to be 
small... how small is hard to say..
  what would be the energy difference per atom if you do bulk FCC vs 
bulk HCP ? Is there some experimental number you can compare with?
  being the difference so small every convergence parameter (cutoff, 
k-point, smearing width) may affect the result... and the overall 
accuracy of the XC functional may be questionable...  probably the final 
conclusion will be that the two sites are almost degenerate
stefano

Wong Kelvin wrote:
> Dear all,
>
> I calcuated the total energy of Cu (111) surface {4 atom per layer, six
> layer with bottom 3 layer fixed, 11 A vacuum layer) with one additional Cu
> atom on FCC and HCP sites.
> (using Cu-PBE-d-rrkjus.UPF, 30 and 300 Ry for energy and rho cutoff. 7x7x1 0
> 0 0 auto kmesh.)
> The difference in total energy of whole cells is only about 6 meV which
> seems to be too small. Pease comment, on the validity of this result.
>
> Wong KC
> NTU singapore
>
>   
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