[QE-users] cell_dofree = 'volume'

[Carlo Nervi]

Dear QE community,
I apologize if this topic has been already discussed in the past.
I'm using QE 6.4.1.
I'd like to perform vc-relax calculations, but keeping strictly fixed the
symmetry of the crystal.
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/
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