epsil (default=.false.) - if .true. in a q=0 calculation for a non metal the macroscopic dielectric constant of the system is computed. Do not set epsil to .true. if you have a metallic system or q/=0: the code will complain and stop
So, if you like to exclude the electric field contribution in semiconductors (insulators) just consider them as a metallic system. But later you will find an inconsistency between phonons you calculated and experimental data as the electric field leads to splitting of LO-TO modes in semiconductors. > I am new to pwscf Welcome! Bests, Eyvaz. ------------------------------------------------------------------- Prof. Eyvaz Isaev, Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia, Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden Condensed Matter Theory Group, Uppsala University, Sweden Eyvaz.Isaev at fysik.uu.se, isaev at ifm.liu.se, eyvaz_isaev at yahoo.com --- On Wed, 9/3/08, Ravi Maranganti <ravitri2k at gmail.com> wrote: > From: Ravi Maranganti <ravitri2k at gmail.com> > Subject: [Pw_forum] How to calculate real space inter-atomic force constants > excluding the contribution due to macroscopic electric field > To: pw_forum at pwscf.org > Date: Wednesday, September 3, 2008, 10:05 PM > 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 > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum
