[Pw_forum] different PP gives different result, why???

[Lorenzo Paulatto]

On 02/05/2014 10:56 AM, Ganjar Kurniawan wrote:
> I am trying to compare the calculation of the Lithium bulk system 
> which has BCC structure with lattice constant is 6.597 bohr using 
> different pseudopotential between Li.pbe-s-rrkjus_psl.0.2.1.UPF and 
> Li.pw91-n-van.UPF.
>
> the result give different of total energy are -14.82521305 Ry and 
> -1.82426227 Ry respectively...
>
> The question is why this is happen??? anyone can to explain it???
>
Dear Ganjar,
as often repeated, the absolute value of the total energy has no meaning 
in periodic boundary condition and pseudopotential calculations. Only 
relative energy, computed with strictly the same setup have physical 
meaning.

I.e. in your case you an compare the energy of bulk Lithium with that of 
isolated Lithium atoms, computed with the same pseudo and cutoff. This 
would give you the binding energy of your crystal.

kind regards

-- 
Dr. Lorenzo Paulatto
IdR @ IMPMC -- CNRS & Université Paris 6
+33 (0)1 44 275 084 / skype: paulatz
http://www-int.impmc.upmc.fr/~paulatto/
23-24/4é16 Boîte courrier 115, 4 place Jussieu 75252 Paris Cédex 05

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