[Pw_forum] How to calculate real space inter-atomic force constants excluding the contribution due to macroscopic electric field

[Ravi Maranganti]

Hello All
   How should i calculate the real space interatomic force constants with
the contribution due to the macroscopic electric field being excluded.
According to Giannozzi et al (Ab initio calculation of phonons in
semiconductors, Phys Rev B, v. 43, p.7231), the contribution to the
dynamical matrix in polar materials can be written as a combination of an
analytical term and a non-analytical term (at low k-vectors). The
non-analytical term involves the Born effective charges and the dielectric
constant. so, should i subtract this term from the dynamical matrix at all
k-vectors (or only at certain k-vectors?) and then use q2r.x to obtain the
real space force constants? Also, should i *not* specify .epsil. = true?  I
am new to pwscf so please bear with me...thanks!

Ravi Maranganti,
PhD Candidate, Mechanical Engg Dept,
Univ of Houston, TX
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