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

[Cyrille Barreteau]

Dear  Wong Kelvin

In copper the difference of energy for an adatom in fcc or hcp is very 
small, see for example:
http://prb.aps.org/abstract/PRB/v70/i7/e075415

6 mev seems a very reasonable number.

cyrille

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Stefano de Gironcoli wrote:

>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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