[Pw_forum] Relaxation of Na(100)

Stefano de Gironcoli degironc at sissa.it
Wed Oct 17 15:05:36 CEST 2007

on the basis of the forces you have reached and an estimate of the 
first-nearest neihgbour interatomic force constant (that you can infer 
from Na typical phonon frequencies) could you please post an estimate of 
the effect that a residual force of 0.0005 Ry/a.u. makes on a) the 
interatomic distance b) the total energy of the system ?
stefano de Gironcoli - SISSA and DEMOCRITOS

naser zare wrote:
> Dear all
> Hello
> I am studying about relaxation of Na(100) .I use "GGA(PBE)" for XC .I 
> have worked on that issue(relaxation) with k-point mesh equal 
> 32×32×1 ,and Ecut range of 25 to 35Ry for wavefunction and 
> Ecut=140Ry up to 350 Ry for charge density .I run program based on 
> presented ranges ,and also used two smearing model(gauss and 
> methfessel-paxton). However,forces had not been reach below 0.0001 
> Ry/a.u ,but approximately 0.0005 Ry/a.u . It should be stated that I 
> reduced dt from 20.DO to 2.D0 step by step in relaxation ,but I have 
> not reached forces below 0.0001 Ry/a.u yet.
> I should state that I have this difficult for slab with 7 layers and 
> more, that number of atoms in supercell is more than 7 atoms.
> I should state that my main question is about reaching 0.0001 Ry/a.u 
> and what can I do for that?, and I was wondering if you could help me. 
> Thank you for your attention.
> Best regards,
> Nasser Zare Dehnavi
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