The ABINIT Users Mailing List ( CLOSED )

[Xavier Gonze <gonze@pcpm.ucl.ac.be>]

On 14 Sep 2006, at 18:08, aaz85 wrote:

> Greetings.
>
> First, please allow me to extend my apologies for any troubles this  
> letter may cause.
>
> I used ABINIT for the calculation of thermodynamic properties of  
> compressed aluminum. If I correctly understand, I should to use
> Unit cell volume ucvol=  6.0972500E+00 bohr^3
> Pressure=  2.2056E+04 GPa
> in output file to get p(V) dependence in case physical temperature  
> is close to zero. My results represent in image.jpg. As you can see  
> results obtained with the help of ABINIT for high compressed  
> aluminum strongly differ from data in cited articles.
> I'd like to ask your help in this case.

Dear Andre,

Did you check the convergence of your data with respect to the number  
of k points ?
You are only using 2 k points, and this might be much too low for  
this metallic system.
Do not forget to check the convergence also with respect to tsmear .

Another potential problem : note that in your input file, you are  
trying to define an optimization
of the cell (using ionmov 3, optcell 3, ntime 10), but your criterion  
to be fulfilled is the default
one (based on tolmxf : the Broyden algorithm stops when the forces  
are sufficiently low),
and the latter is totally ineffective for this highly symmetric
structure, in which there is no force on each atom, due to symmetry  
reasons.
So, ABINIT performs only one Broyden step, and stops immediately after.
Still, your SCF convergence is adequate, and the couple that you  
indicate
> Unit cell volume ucvol=  6.0972500E+00 bohr^3
> Pressure=  2.2056E+04 GPa
is likely correct (if one forgets about the potential convergence  
problem highlighted above)

Finally, since you are studying highly compressed crystals, you  
should worry about your
pseudopotential. You are using 13al.981214.fhi , but I would bet this  
potential
has a core that is rather extended, so that under pressure, the cores  
overlap .
For your study, I encourage you to generate yourself your  
pseudopotential :
you should make sure that the cut-off radius is sufficiently small  
that the different
pseudization spheres do not overlap...
This is a specific caution that people working with highly compressed  
state of matter
should take.

Good luck,
Xavier