[QE-users] cell_dofree = 'volume'

[Paolo Giannozzi]

On Sat, Jul 6, 2019 at 11:31 AM Carlo Nervi <carlo.nervi at unito.it> wrote:

I'd like to perform vc-relax calculations, but keeping strictly fixed the
> symmetry of the crystal.
>

not sure I understand: if the starting structure has the desired crystal
symmetry, the final structure will - apart from unfortunate or pathological
cases - have the same symmetry

Paolo




> I supposed that the keyword
> cell_dofree='volume'
> should be the right option to use, but pw.x exit complaining that
> cell_dofree='volume' can be used only if ibrav=1.
> Is there any technical reasons for this?
> I was supposing that simply changing only celldm(1) should work.
>
> I tried, as alternative, cell_dynamics='damp-w', which apparently keep
> almost the symmetry (but not strictly), but it shows an extremely slow
> convergence (in my molecular crystal vc-relax converge in 17 bfgs steps,
> while the damp-w vc-relax calculation is currently running the 127th step).
>
> Thank you,
> Carlo
>
> P.S.: I suppose that simple deleting the below bold rows in cell_base.f90
> (subroutine init_dofree) would not work..
>
>             CASE ( 'volume' )
>               !CALL errore(' init_dofree ', &
>               !   ' cell_dofree = '//TRIM(cell_dofree)//' not yet
> implemented ', 1 )
>  *             IF ( ibrav /= 1 ) THEN*
> *                CALL errore('cell_dofree', 'Isotropic expansion is only
> allowed for ibrav=1; i.e. for simple cubic', 1)*
> *              END IF*
>               iforceh      = 0
>               iforceh(1,1) = 1
>               iforceh(2,2) = 1
>               iforceh(3,3) = 1
>               isotropic    = .TRUE.
>
> --
>
> ------------------------------------------------------------
> Prof. Carlo Nervi carlo.nervi at unito.it  Tel:+39 0116707507/8
> Fax: +39 0116707855      -      Dipartimento di Chimica, via
> P. Giuria 7, 10125 Torino, Italy.    http://lem.ch.unito.it/
>
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso)
> users mailing list users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users



-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20190708/11633afe/attachment.html>