[Pw_forum] LDA, PBE and PBEsol and Cohesive energy

[Elliot Menkah]

Thanks Giuseppe.
I think tested for the convergence of ecutrho (as I had not done that
earlier) to obtain an optimum value which is actaully giving good
results in comparison to experimental data.


On 10/23/2014 11:56 AM, Giuseppe Mattioli wrote:
> 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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-- 
Elliot S. Menkah
Research Student - Computational Chemistry/ Computational Material Science
Theoretical and Computational Chemistry
Dept. of Chemistry
Kwame Nkrumah UNiversity of Sci. and Tech.
Kumasi
Ghana

Tel: +233 243-055-717

Alt Email: elliotsmenkah at gmail.com
           elliotsmenkah at hotmail.com