[Pw_forum] Order of Total Energy in SCF calculations

[Lorenzo Paulatto]

On 12/20/2013 02:54 AM, Manu Hegde wrote:

> !    total energy              =    4948.67653659 Ry
>      Harris-Foulkes estimate   =    4948.67653659 Ry
>      estimated scf accuracy    <          2.7E-14 Ry
> 
>      The total energy is the sum of the following terms:
> 
>      one-electron contribution =    -418.28824981 Ry
>      hartree contribution      =     172.04233534 Ry
>      xc contribution           =     -53.20237765 Ry
>      ewald contribution        =    5304.14344253 Ry
>      one-center paw contrib.   =     -56.01162391 Ry
>      smearing contrib. (-TS)   =      -0.00698992 Ry


You have a very high repulsive Ewald (i.e. Ion-Ion) contribution. This
may be a problem with the pseudopotential or may very well be normal. I
remind you that absolute energies have no meaning in periodic boundary
conditions. You should compute the binding energy of this compound
w.r.t. its elements (i.e. 3x O2 molecule + 1/2 Gallium unit cell)


> ATOMIC_SPECIES
>    Ga   31.00000  Ga.pbe-mt_fhi.UPF
>     O    8.00000  O.pbe-kjpaw.UPF

Just to point out that 31 and 8 are not the atomic masses of Gallium and
Oxygen, they are their atomic numbers. This won't make a difference
unless you compute phonons or simulate molecular dynamics

cheers


-- 
Dr. Lorenzo Paulatto
IdR @ IMPMC -- CNRS & Université Paris 6
phone:+33 (0)1 44275 084 / skype: paulatz
www:  http://www-int.impmc.upmc.fr/~paulatto/
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