[Pw_forum] original symmetry operations not satisfied

[Ion Errea Lope]

Dear all,

Lately, I am trying to relax a body centered tetragonal structure with
16 atoms per cell using a 'relax' calculation in order to minimize the
forces for future phonon calculations.

Here is my input:

 &control
    calculation='relax'
    restart_mode='from_scratch',
    prefix='ca',
    dt = 40.0,
    etot_conv_thr = 1.0D-5 ,
    forc_conv_thr = 1.0D-4 ,
    tstress = .true.
    tprnfor = .true.
 ...
 /
 &ions
    ion_dynamics = 'damp'
    pot_extrapolation = 'first_order' ,
    wfc_extrapolation = 'first_order' ,
 ...
ATOMIC_POSITIONS {crystal}
...
Ca    0.50000    0.81573    0.01829   0  1  1
Ca    0.50000    0.51829    0.31573   0  1  1
Ca    0.50000    0.48171    0.68427   0  1  1
Ca    0.50000    0.18427    0.98171   0  1  1 
 ...

Once the first scf calculation is done and the new coordinates
calculated, I get the following error message in the output file:

ATOMIC_POSITIONS (crystal)
...
Ca       0.500116912   0.815774675   0.018451586    0   1   1
Ca       0.499883088   0.518568498   0.315891586    0   1   1
Ca       0.500116912   0.481431502   0.684108414    0   1   1
Ca       0.499883088   0.184225325   0.981548414    0   1   1


  SYMMETRIZED ATOMIC COORDINATES)

ATOMIC_POSITIONS (crystal)
...
Ca       0.500000000   0.815803903   0.018539270    0   1   1
Ca       0.500000000   0.518539270   0.315803903    0   1   1
Ca       0.500000000   0.481460730   0.684196097    0   1   1
Ca       0.500000000   0.184196097   0.981460730    0   1   1



 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%
     from checkallsym : error #         1
     some of the original symmetry operations not satisfied
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%

     stopping ...

Apparently, after the symmetrized atomic coordinates are written the
calculation stops without proceeding with the next scf calculation.

I have checked the mail list and realised more people encountered this
problem. Some of the proposals I found mentioned trying with different
ion_dynamics (bfgs and damp), changing first order extrapolation to
second order and finally, using different number of processors. I have
tried both bfgs and damp calculations, fisrt order and second order
extrapolation, and also calculations with different numbers of
processors. However neither of them worked in my case and the same error
was found.

Another option is not to consider symmetry operations including the flag
no_sym = .true. Although this works correctly and relaxes the structure
(taking much longer though due to the larger number of kpoints) does not
keep the atoms at the symmetry point 0.5. 

I wonder if there is any option to make the relaxation in y and z
coordinates without relaxing in x, that is, keeping symmetry operations
but without having this error. 

Thanks in advance and kind regards,

Ion


-- 
========================================
 Ion Errea Lope
 Materia Kondentsatuaren Fisika Saila
 Zientzia eta Teknologia Fakultatea
 Euskal Herriko Unibertsitatea
 644 Posta Kutxatila, 48080 Bilbo, Spain

 Telefonoa: +34 946015322
 Mail: ierrea001 at ikasle.ehu.es
========================================