Dear users and developers, Running the ph.x one can extract the charge density response (fildrho) due to a phonon mode for an arbitrary phonon wave vector q. Thereafter one can presumably use pp.x to plot the induced charge density corresponding to mode in 1D, 2D or 3D (xcrysden).
When this is done, the density is plotted for the super-cell no matter at which phonon wave vector q the linear response calculation was done. Then, I wonder if it is possible to obtain (visualizing, say with pp.x) the charge density of the corresponding wavelength? For example: One calculates a phonon mode with a wavelength which is twice the periodicity of the undistorted lattice in a particular direction. Let say that a top atom (in a surface slab) vibrates in the z-direction. Then when visualizing the charge density response for this mode in a 2D- plane along the wave vector, the first atom moves in the positive z- direction giving rise to a charge density pattern, then moving along the corresponding wave vector, the next surface atom should move in the negative z-direction giving rise to a charge density pattern with opposite sign. Although when extracting the above with pp.x and xcrysden, the charge density is just repeated (with the same sign) for the forthcoming atoms. It looks to me that the code consider the phonon induced density in the same way as a ground state density and thus benefiting from the symmetry of the unperturbed lattice. However, when a displacement field it set up by a phonon mode with a wave vector in the surface Brillouin zone this symmetry is broken and the periodicity deviates from the periodicity of the undistorted lattice. The information of the induced density variation caused by a phonon mode at an arbitrary q-vector should be possible to extract from a linear response calculation. The question is HOW? Looking forward to any replies. Best regards Vasse Chis -- Vasse Chis, Ph.D Student Department of Physics G?teborgs Universitet Fysikg?rden 6B S-412 96 G?teborg, SWEDEN tel :+46 (0) 31 7723338 email :Vasile.Chis at physics.gu.se
