The ABINIT Users Mailing List ( CLOSED )

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

Hi,

If I understand correctly you are using the exact same structure in both case 
?
The only difference being the use of variables needed by the cell
optimization in one case ?
For instance you are likely using ecutsm ?

If everything preceding is correct, is it possible that your cutoff
energy is not converged ? Or at least and more precisely  that the
stress is not converged with respect to the cutoffenergy to 5e-6
Ha.bhr^-3 ?
In this case it would be a nice explanation for your problem and you
would have to check again the level of convergenc you had with respect
to ecut and k-point and perform again your optimization if the
pressure you want is really of the order ot 1e-3 GPa. Or you can just
keep using the same ecutsm knowing that your calculation is not
perfectly converged ...

regards

PMA



On Fri, May 16, 2008 at 11:03 AM, Manuel Pérez Jigato
<Manuel.PerezJigato@fys.kuleuven.be> wrote:
> Dear all
>
> after computing the optimal volume/lattice constant of a rock-salt oxide for
> a fixed k-point set and planewave cut-off energy,
>
> 1- if i then carry out a total energy calculation for the optimal lattice
> constant
> 2- and if i start the volume/lattice constant optimisation starting from the
> same
>  optimal lattice constant
>
> in both cases i get completely different stress: please see numbers below
>
> let me ask, is the difference explained by the absence of the cut-off
> smoothing
> in the total energy calculation, and that is used during cell optimisation
>
> thanks
>
> Manuel Perez Jigato
>
> -----------------------------------------------------------------------------
>
> 1- total energy calculation
>
>  Cartesian components of stress tensor (hartree/bohr^3)
>  sigma(1 1)=  4.90452484E-05  sigma(3 2)=  0.00000000E+00
>  sigma(2 2)=  4.90452484E-05  sigma(3 1)=  0.00000000E+00
>  sigma(3 3)=  4.90452484E-05  sigma(2 1)=  0.00000000E+00
>
> -Cartesian components of stress tensor (GPa)         [Pressure= -1.4430E+00
> GPa]
> - sigma(1 1)=  1.44296084E+00  sigma(3 2)=  0.00000000E+00
> - sigma(2 2)=  1.44296084E+00  sigma(3 1)=  0.00000000E+00
> - sigma(3 3)=  1.44296084E+00  sigma(2 1)=  0.00000000E+00
>
>
> 2- cell-optimisation
>
>  Cartesian components of stress tensor (hartree/bohr^3)
>  sigma(1 1)=  1.25262834E-07  sigma(3 2)=  0.00000000E+00
>  sigma(2 2)=  1.25262834E-07  sigma(3 1)=  0.00000000E+00
>  sigma(3 3)=  1.25262834E-07  sigma(2 1)=  0.00000000E+00
>
> -Cartesian components of stress tensor (GPa)         [Pressure= -3.6854E-03
> GPa]
> - sigma(1 1)=  3.68535934E-03  sigma(3 2)=  0.00000000E+00
> - sigma(2 2)=  3.68535934E-03  sigma(3 1)=  0.00000000E+00
> - sigma(3 3)=  3.68535934E-03  sigma(2 1)=  0.00000000E+00
>
>
> Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm
>
>



-- 
Pierre-Matthieu Anglade