[Q-e-developers] D3.x limited to Gamma?

[Badescu, Catalin S Ctr USAF AFRL/RYDD]

Dear colleagues,

My name is Stefan Badescu.  I am trying to understand a detail of the D3
suite. Some literature suggests that it can be used to calculate the decay
of phonons at any q-point. My first interpretation of the input required by
d3.x is that it works for Gamma phonon decaying through a q,-q channel.

In the calculation of force constant derivatives, the d3.x program requires
the perturbed densities at q0=0 and at the q of interest. My understanding
is that this produces V^(3)(0,q,-q) . To do this at a point different from
Gamma, that is, to calculate V^(3)(k,q+k,-q), can we input to the program
program  fildrho given by a calculation at q+k, and  fild0rho given by a
calculation at k? Would this make any sense, i.e., is the resulting V^(3)
appropriate to calculate the decay of a k phonon through a q+k and a -q
channel? 

The program runs with this input but I am not sure if it is meaningful.

Thank you for your consideration. Sincerely,

--Stefan
PS. I had an account on the forum but I changed my job and email address
meanwhile. I am updating it on the pwscf forum but I thought the question is
quite technical anyway therefore I wrote first to this address.

 

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