[QE-users] phonons with vdW functional

[Aleksandra Oranskaia]

Hello dear users and developers of QE,

I am trying to calculate phonons using very good structure (tightly optimized, matching the experimental one, etc), but whatever I do the result is:

 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
     Error in routine cdiaghg (448):
     S matrix not positive definite
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

I varied:
- number of processors (with too large # of processors similar issues are reported)
- ecutrho increasing it up to ecutwfc*15
- different smearings schemes (the system is a narrow band gap semiconductor)
- different diagonalization procedures (from my personal experience: david fail sometimes where cg saves the day)
- used nosym=.true.

I would highly appreciate any thoughts on the nature of this mistake happening in the very beginning of phonon calculation.


Best,
Alex.
___
Aleksandra Oranskaia (M.Sc.)
ChemS PhD student, KAUST
Phone: +966 50 1335254







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