The ABINIT Users Mailing List ( CLOSED )

["Anglade Pierre-Matthieu" <anglade@gmail.com>]

Hi,

I'm not that sure I understand the way you proceed to compute cohesive
energy. Usualy people do the following:
Find the equilibrium cell parameter of the structure of interest with
every approximation you want (pseudopotential, GGA/LDA/..., T
smearing, spin polarization (colinear, none, not colinear) ...)
Within the same approximations increase the cell size up to "infinity"
and get the cohesive energy from the difference:
E_coh=+/-  E_eq -E_inf

Hope this helps

regards

PMA

On 8/29/06, LEE Chin Chai <cc-lee@imre.a-star.edu.sg> wrote:
> Dear all ABINIT users,
>
>
>
> Currently, I am trying out to test out a few pseudopotential files (GGA.fhi
> format) for Co, Si, O and Ni before doing some supercell relaxation. But I
> have some problems in calculating their respective cohesive energy. I
> started on Si first as there is a tutorial that guides me (new user) along
> to use abinit. In order to calculate the cohesive energy for Si, I would
> have to calculate ground state energy of a Si atom. Can some one please
> guide me on how to set the parameter for the input file for the calculation
> of ground state energy of an atom? Is it a must to state their occupancy in
> order to obtain the correct the ground state energy? If so, please give me
> some points on how state the occupancy for different elements. Is it
> possible to do such calculation by setting nsppol to 2 only?
>
>
>
> I am using Abinit version 4.6.5. When I tried using nsppol to 2, the ground
> state energy for Si is about -3.738 Hartree while the total energy for the 2
> atoms primitive unit cell for Si is about -7.8761Hatree. So the cohesive
> energy (E_coh = E_tot – 2*E_Si_atom) that I obtained is about 0.4001 Hartree
> and it is far too big. If I am not wrong, the ground state energy that I
> have calculated is wrong. But where have I gone wrong, please kindly advise.
> Thank you.
>
>
>
> Cheers,
>
> ChinChai
>
>
>
>
>
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--
Pierre-Matthieu Anglade