[Pw_forum] vc-relax with atomic position fixed.

[Dr. B.R.Sahu]

Hi

 thanx

  I noticed that use of vc-relax where the lattice paramters and atomic
positions are relaxed simultaneously, it takes large number of ionic
iterations to converge say 500(ofcourse it depends on the type of atoms,
force and energy tolerence, number of k-points, cutoff etc). But is there
a way to accelerate the convergence cycle say using the option 'dt='
in the input file.

In list of test example with the source code, example 3( for the Al(001)
slab relaxation using "relax" dt=120 is used.

How does "dt' the time step influences the relaxation in both relax
and vc-relax? 

what value is appropriate?

regards
sahu


> >
> with the variable cell relaxation option you can look for combined 
> relaxation of atomic positions and cell at a fixed pressure (not 
> volume... the two things are of course related)
> 
> If the positions are already correct (for symmetry reasons) then the 
> internal forces acting on them should vanish and they will not 
> participate in the relaxation.
> 
> stefano
>