[Pw_forum] Issues with Phonons

[Thierry Tsafack]

Dear fellow QE users,

I hope this email finds you well.

Could you please help me fix the issues below?

1-) The executable ph.x requires the knowledge of nq1 nq2 nq3 to  
determine the density of the Monkhorst-Pack grid, i.e, number of  
points and their coordinates.  What is the linkage between nq1 nq2 nq3  
and the number of points in the grid?

Everything else being equal, 3x3x1 yielded 5 points, 4x4x1 yielded 10  
points, 5x5x1 yielded 13 points, 6x6x1 yielded 20 points, 7x7x1  
yielded 25 points.

For benchmark purposes, how do I know how many points nq1 x nq2 x 1  
will produce without doing the calculations?

  2-) How to go about a situation in which ph.x produces w(q_i)>0 for  
all i in the above grid, but q2r.x and matdyn.x produce some w(q_i)<0,  
for all choices of the ASR or ZASR?  Assume the geometry relaxation  
was done as well as the scf calculation and you know that the  
structure is stable.

3-) Recover =.true. in QE-4.3 always fails saying:"from checkallsym :  
error".  How to go around it?

Thanks in advance for your clues, if your answer necessitates further  
details, let me know.


~Thierry T.
MEMS Rice University, Houston, TX