On Tue, 21 Nov 2006, marcel wrote: | Dear All, | | I'm doing some test calculations on bulk hexagonal CdSe. I want to calculate | the phonon dispersion. | (Im using the version of T. Archer, for LO-TO splitting and include BC in my | Siesta calculation. | The dielectric constants I use are from literature on measurements. ) | | I get perfect acoustic frequencies at 0.0 cm^(-1). | Lowest optical and highest optical frequency are underestimated by max. 2 % | from experiment. OK. | However, the mid-range frequencies are overestimated, up to 10%. | | So would you think this is ok, or should I further investigate the source of | this discrepancy?
Marcel: it can be deduced from your message that you have this problem already in Gamma, and for the minimal cell. Did you check the effect of k-mesh? The forces and force constants may vary with it. Andrei Postnikov +-- Dr. Andrei Postnikov ---- Tel. +33-387315873 ----- mobile +33-666784053 ---+ | Paul Verlaine University - Institute de Physique Electronique et Chimie, | | Laboratoire de Physique des Milieux Denses, 1 Bd Arago, F-57078 Metz, France | +-- [EMAIL PROTECTED] ------------ http://www.home.uni-osnabrueck.de/apostnik/ --+
