[Pw_forum] vc-md question

Stefano de Gironcoli degironc at sissa.it
Tue Jan 31 09:22:15 CET 2006


As Paolo say vc related things are far from optimal... however it is 
possible tu use it to perform structural relaxation
at finite pressure using it.

Check information about namelist &CELL in file Doc/INPUT_PW

calc='vc-md' performs variable cell  MD (no damping) at the pressure 
specified by the variable press (in Kbar) in namelist &CELL using either 
Parrinelllo-Raman or Wentzcovitch extended lagrangian ( specified as 
cell_dynamics='pr' or cell_dynamics='w' ).
BEWARE default value of cell_dynamics is NONE even if calc='vc-md'.

calc='vc-relax' performs relaxation by  damped dynamics using either 
Parrinello-Raman or Wentzcovitch extended lagrangian 
(cell_dynamics='damp-pr' or 'damp-w' ... againg default is NONE) at the 
pressure specified by press.

stefano


Miguel Martínez Canales wrote:

> Hi again, Paolo
>
>> I think that there is presently no check on convergence, so if you 
>> keep sending jobs, it will keep running. Does it converge or not?
>
>
> Ok, so there is no check. I should have known better. Use the source, 
> Luke.
> Regarding convergence, it starts closing (slowly if dt is not good,
> obviously) and then it oscillates. Or that is what it seems. Some 
> output at
> the end of the e-mail.
>
>> By the way, there is also a 'vc-relax' option that is supposed to 
>> perform structural optimization. I am not sure if vc-md can
>> actually do damped dynamics
>
> I understood that vc-relax fully relaxes the structure. I mean, the 
> target
> pressure of the relaxation is p=0. That is why I used vc-md. How do you
> compute equations of state for noncubic cells? Because maybe I am working
> in a very ineffective way.
>
> Oh! and vc-md not being damped might explain the following output:
>
> Input is the same as in first e-mail, but dt=100 (note: dt=150 leads to
> structure deestabilisation) and the following &system flags and 
> ATOMIC_POS:
>





More information about the Pw_forum mailing list