The ABINIT Users Mailing List ( CLOSED )

["LEE Chin Chai" <cc-lee@imre.a-star.edu.sg>]

Hi Anglade Pierre-Matthieu,

I did find the equilibrium cell parameter of the structure. 
I don't quite get your second point. Do you mean by increasing the
equilibrium cell parameter to "inifinity"? 
Take for example in tutorial 3, within LDA, the equilibrium cell
parameter is found to be 10.217Bohr. In order to obtain to E_inf, the
cell parameter is increased to say about 30 Bohr and then calculate the
total energy of the system.

Cheers,
ChinChai 

-----Original Message-----
From: Anglade Pierre-Matthieu [mailto:anglade@gmail.com] 
Sent: Tuesday, August 29, 2006 6:18 PM
To: forum@abinit.org
Subject: Re: [abinit-forum] FW:Cohesive Energy

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
>
>
>
>
>
> **********************************************************************
>  This email and any files transmitted with it are confidential and
>  intended solely for the use of the individual or entity to whom they
>  are addressed. If you have received this email in error please notify
>  the system manager or the sender.
>
>  Institute of Materials Research and Engineering -
> http://www.imre.a-star.edu.sg
> **********************************************************************
>


-- 
Pierre-Matthieu Anglade