[Pw_forum] Help about vc-relax

[Stefano de Gironcoli]

The problem is that symmetry is a properties of the structure and PR has 
broken it so you
cannot continue the broken run, even by damp-w.
You can of course start from scratch  using the "broken" structure.
The code will find less symmetry w.r.t. to the original run, will 
generate the needed k-points and will go on.

About your question on why PR braek the symmetry... there is a 
discussion of this problem in Renata Wentzcovitch's original work

 *Invariant molecular-dynamics approach to structural phase transitions 
<http://prola.aps.org/abstract/PRB/v44/i5/p2358_1?qid=1333169f7de9ff4e&qseq=33&show=10>*
 R. M. Wentzcovitch
 Phys. Rev. B *44*, 2358-2361 (1991)

stefano



You Lin wrote:

>Dear Paolo:
>
>Still got a question: After my first run, I wish to start a from the 
>silicon.save by changing the control option:
>
>restart_mode='restart'
>
>Then the the code reported:
>
>     Program PWSCF     v.3.0    starts ...
>     Today is  4Dec2005 at 19:42: 4
>
>     Ultrasoft (Vanderbilt) Pseudopotentials
>
>     Current dimensions of program pwscf are:
>
>     ntypx = 10   npk = 40000  lmax =  3
>     nchix =  6  ndmx =  2000  nbrx = 14  nqfx =  8
>
>     Starting configuration read from file   silicon.save
>
>     Reading file silicon.save
>     warning: symmetry operation # 25 not allowed.   fractional 
>translation:
>       0.2578067  0.2525927  0.2401578  in crystal coordinates
>
> 
>%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>     from checkallsym : error #         1
>     not orthogonal operation
> 
>%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>
>     stopping ...
>---------------- End of output --------------------------------
>
>The symmetry is wrong again? I was using symmetry-conserving algorithm: 
>the Wentzcovitch algorithm (cell_dynamics='damp-w'). And it runs fine
>if I start from scratch.
>
>Thanks for the help in advance.
>
>________________________________________
>
>You Lin
>
>Department of Physics
>University of South Florida
>4202 East Fowler Avenue
>Tampa, FL 33620
>________________________________________
>
>Tel: (813)396-9220 [Office]
>
>Homepage: http://shell.cas.usf.edu/~ylin
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>
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