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[zhangting <zhangting@pku.edu.cn>]

Dear Erik Ylvisaker:

     Thanks very much for your replying my question. When I use "shiftk 0.5 
0.5 0.5", the mismatch, of which the number of

K-points between the datasets with & without time-reversal symmetry, do 
disappear. But there immediately appears another

trouble in the calculation, the code escapes with such messeges:
-------------------------------------

 inwffil: ERROR                                                  
 The file phonono_DS1_WFK cannot be used to start the
 present calculation. It was asked that the wavefunctions be accurate, but
 at least one of the k points could not be generated from a symmetrical one.
 dksqmax=    3.331709E-04                                        
 Action: check your wf file and k point input variables.

 leave_new : decision taken to exit ...                          

--------------------------------------

      This error occurs at the q= 0.8333 0.8333 0.8333, or the 4th dataset, 
while the phonon at Gamma is correctly

completed. What does this message mean? Should I increase the q-point mesh to 
8x8x8 or should I do something else?

The q-point is generated with scheme in the trf2_2.in, and the k-point 
density is 6x6x6. shiftk here is set to 0.5 0.5

0.5. The .in files are attached.


======================================================================================
         think this happens because you are using shiftk 0 0 0.  Time 
reversal symmetry allows half the Brillouin zone to not be calculated.  But 
without a shift, you end up picking points like Gamma, which has no time 
reversed point, and points at the zone surface, whose time reversed point is 
separated by a reciprocal lattice vector, so it can't be eliminated by time 
reversal symmetry because the choice of grid didn't include it.  I think if 
you set shiftk to 0.5 0.5 0.5 you will see the results you expect.


                                

　　　　　　　　zhangting
　　　　　　　　zhangting@pku.edu.cn
　　　　　　　　　　2006-05-11

Attachment: qpoint.in
Description: Binary data

Attachment: phonon.in
Description: Binary data