Dear Dr. Gunnar Palsson, > I was wondering if turboEELS or some other aspect of TDDFT generalised to > extended systems can calculate the off-diagonal elements of the dielectric > tensor, for instance epsilon_xy?
The turboEELS code allows one to compute the loss function -Im[1/eps(q,w)], where q is the transferred momentum, and w is the frequency. Depending on the direction of the transferred momentum q in the Brillouin zone and depending on its modulus |q|, the value of the loss function changes. The code works with finite values of q (q=0 is not allowed, but only small values of q can be considered, q->0). From the knowledge of 1/eps(q,w) it is possible to compute eps(q,w). Conversely, the epsilon.x code works for q=0, and it allows one to compute the dielectric matrix/tensor eps_ij(q=0,w), where i and j are the Cartesian indices X,Y,Z (see notes espresso/PP/Doc/eps_man.tex). In particular, see equation after Eq.(10), and also see Eq.(11) [in order to understand why it is a matrix and not a function]. Moreover, epsilon.x is based on the independent particle approximation, while turboEELS is based on TDDFPT which includes Hartree and exchange-correlation interactions. Concerning your question: I am not sure, but it seems to me that if one considers the TDDFPT formalism of turboEELS exactly at q=0 (this limit must be implemented) one should obtain the inverse and direct dielectric *matrices*. I have to admit I have never thought in detail about this. HTH Regards, Iurii -- Dr. Iurii Timrov Postdoctoral Researcher Swiss Federal Institute of Technology Lausanne (EPFL) Laboratory of Theory and Simulation of Materials (THEOS) CH-1015 Lausanne, Switzerland +41 21 69 34 881 http://people.epfl.ch/265334 ________________________________________ From: [email protected] <[email protected]> on behalf of Gunnar Karl Pálsson <[email protected]> Sent: Saturday, August 26, 2017 7:07 PM To: PWSCF Forum Subject: [Pw_forum] Off diagonal elements of the dielectric function using turboEELS Hi all, I was wondering if turboEELS or some other aspect of TDDFT generalised to extended systems can calculate the off-diagonal elements of the dielectric tensor, for instance epsilon_xy? The reason I am interested in the off-diagonal components is for the calculation of the Magneto-Optical Kerr rotation angle which is proportional to this quantity. If it does not, is this a straight forward extension that could be done or is there some inherent limitation? I see that it is possible to calculate these components with epsilon.x using the 'offdiag' flag. For cubic systems the off-diagonal elements are probably zero but in the presence of spin-orbit coupling for a magnetic material like bcc iron it could be possible to calculate given that turboEELS has nicely been extended to metals and can deal with spin-orbit coupling? Best regards, Dr. Gunnar Palsson Researcher Department of Physics and Astronomy Uppsala University Sweden _______________________________________________ Pw_forum mailing list [email protected] http://pwscf.org/mailman/listinfo/pw_forum _______________________________________________ Pw_forum mailing list [email protected] http://pwscf.org/mailman/listinfo/pw_forum
