[Pw_forum] Relaxation doesn't converge

[Pablo Aguado]

I'm sorry, but I still can't see the problem ...

forc_conv_thr = 1.0d-3  is satisfied ==> conv_ions = true

Only z is allowed to relax (cell_dofree = 'z') so:
sigma_xx & sigma_yy should be set to 0 at some point
sigma = 0.87 Kbar
press_conv_thr = epsp = 1.0 Kbar
press = 0.0

so conv_ions.AND.(ABS( sigma(i,i) - press) * uakbar < epsp) is true,
unless the program is still considering stress_xx and stress_yy
(cell_dofree is not being taken into account)

Pablo


On Wed, Sep 2, 2009 at 1:03 PM, Paolo Giannozzi<giannozz at democritos.it> wrote:
> Pablo Aguado wrote:
>
>> All I can say is that it seems to be converged
>
> "it seems" /= "it is"
>
>> press_conv_thr = 1.0d0
>
> this is internally called "epsp"
>
>>          total   stress  (Ry/bohr**3)                   (kbar)     P=   -0.84
>>  -0.00001150   0.00000000   0.00000000         -1.69      0.00      0.00
>>   0.00000000  -0.00001150   0.00000000          0.00     -1.69      0.00
>>   0.00000000   0.00000000   0.00000591          0.00      0.00      0.87
>
> and this is where the convergence is checked: PW/vcsmd.f90, line 212
> and following:
>
>      DO i = 1, 3
>         !
>         conv_ions = conv_ions .AND. &
>                     ( ABS( sigma(i,i) - press) * uakbar < epsp )
>         !
>         DO j = ( i + 1 ), 3
>            conv_ions = conv_ions .AND. &
>                        ( ABS( sigma(i,j) ) * uakbar < epsp )
>         END DO
>         !
>      END DO
>
> press=external pressure, sigma=stress tensor,
> uakbar=atomic units to KBar conversion factor.
>