[Pw_forum] Problems with vc-relaxed calculation

[Vikas Varshney]

Did you update the cell dimensions correctly? For example, if your
celldm(1) and celldm(3) before relax are a and c. Lets say after
relax, they become 1.1a and 1.2c. In the final scf calculation, new a
should be 1.1a and and new c shsould be (1.2/1.1)*c.

I dont know if this is the case but just wanted to tell that. Not much
help can be done until more input is provided.

Hope this helps
Vikas


On Fri, Jul 1, 2011 at 12:37 PM, WANG Wei <wonvein at gmail.com> wrote:
> Dear QE users,
>
> Why are the total energy and press of the final step of vc-relax
> calculation different from those of the scf calculation using the same
> structure?  Especially for the values of press, what makes this great
> difference between the final step of vc-relax calculation and the final scf
> calculation (after the vc-relax calculation)?
>
> (1) For the final step of vc-relax calculation, the press and total energy
> are:
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
> !    total energy              =     -73.74310183 Ry
>
>           total   stress  (Ry/bohr**3)                   (kbar)     P=
> -0.03
>   -0.00000009   0.00000001   0.00000000         -0.01      0.00      0.00
>    0.00000001  -0.00000008   0.00000000          0.00     -0.01      0.00
>    0.00000000   0.00000000  -0.00000048          0.00      0.00     -0.07
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>
> (2) For the final scf calculations, the press and total energy are:
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
> !    total energy              =     -74.60031750 Ry
>
>           total   stress  (Ry/bohr**3)                   (kbar)     P=
> 638.94
>    0.00760001  -0.00000151   0.00000000       1118.00     -0.22      0.00
>   -0.00000151   0.00759826   0.00000000         -0.22   1117.74      0.00
>    0.00000000   0.00000000  -0.00216804          0.00      0.00   -318.93
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>
> Regards,
> WANG
>
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