[Pw_forum] Third order anharmonic dynamical matrix

[Jonathan Breeze]

Dear PWscf users,

Please excuse my earlier post on the above topic. I had been very silly, 
and not realised that the D3 code only calculated the anharmonic 
coupling coefficients for zone-centre phonons, $D^3(0,q,-q)  Silly me 
indeed!
This leads me onto my next question....

Using the PWSCF D3 code, should it be possible to calculate the 
coefficients for phonons at arbitraty wave-vector?
That is, to calculate D^3(-q1-q2,q1,q2).

Looking at the 2n+1 theory, it should be possible, but also looking at 
the code, it seems formidable.
Any ideas on how to the modify the code (if at all required) to be able 
to do this?

Kind regards,

Jonathan Breeze