[Pw_forum] Anharmonic terms - 3rd order derivatives of energy wrt position

[stewart at cnf.cornell.edu]

Hi all, 

  I am interested in anharmonic properties of crystals and I would like to 
calculate the third order derivatives of energy with respect to changes in 
lattice position.  PWscf does a great job of calculating the interatomic 
force constants.  I was wondering if it is possible to calculate the 3rd 
order terms for arbitrary q,q', and q''.  I have looked at the d3.x code, 
but I believe this program only calculates terms of the form (0,q,-q).  I 
would be interested in any suggestions people have on calculating these 
terms.  Is this feature in the works for PWscf?  Also, can d3.x now handle 
ultrasoft pseudopotentials? 

Thanks in advance for your help! 

Best regards, 

Derek 


################################
Derek Stewart, Ph. D.
Scientific Computation Associate
250 Duffield Hall
Cornell Nanoscale Facility (CNF)
Ithaca, NY 14853
stewart (at) cnf.cornell.edu
(607) 255-2856