[Pw_forum] LDA, PBE and PBEsol and Cohesive energy

[Giuseppe Mattioli]

Dear Elliot

> Problem 1

        Ni.pbesol-n-kjpaw_psl.0.1.UPF
     	ecutwfc      = 40.0
     	ecutrho      = 320.0,

Have you tried to reach convergence wrt ecutwfc and ecutrho? The above Ni PAW pseudopotential (PAW, not US) may require higher cutoffs.

> Problem 2

> I added 15 15 15 Ang to the XYZ Cell parameters and the single atom sits
> in a corner whiles I expect it to sit some where in the middle.

Why? You asked to put it in the corner...

ATOMIC_POSITIONS {alat}
Ni1      0.000000000   0.000000000   0.000000000

HTH
Giuseppe

On Thursday, October 23, 2014 11:17:37 AM Elliot Menkah wrote:
> Hello everyone,
> Problem 1
> ---------------------------------------
> I'm computing for lattice constant and comparing the employment of
> exchange correlation ultra-soft pp such as LDA, PBE and PBEsol. I know
> LDA would underestimate the lattice parameter, PBE would overestimate it
> but PBEsol should do better than PBE.
> 
> My calculations are shows LDA= 3.419  PBE= 3.516 PBEsol = 3.455 Angstom.
> experimnetal value I'm comparing it to is 3.522 Ang
> 
> PBEsol gave a lower atomic lattice value than PBE.
> 
> What could be wrong with the composition of the system?
> 
> Attached is the input file(vc_ni-bulk-pbesol.in) for the PBEsol USPP
> calculations.
> 
> Problem 2
> -------------------------------------------
> Trying to find Cohesive energy and I already have my energy of the bulk.
> I'm now computing for the energy of a single atom in a vacuum system.
> 
> I added 15 15 15 Ang to the XYZ Cell parameters and the single atom sits
> in a corner whiles I expect it to sit some where in the middle.
> 
> What I'm I not doing right please.
> 
> Attached is the respective (evac-ni.in) file too.
> Thank you.
> 
> 
> 
> 
> Kind Regards,
> 
> 
> 
> Elliot

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   Giuseppe Mattioli                            
   CNR - ISTITUTO DI STRUTTURA DELLA MATERIA   
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