Sorry everybody. In a previous post I said: On Jul 23, 2008, at 11:48 AM, Stefano Baroni wrote:
> example 31 deals with bulk silicon, a bulk, nonpolar, system for > which \eps_\infty=\eps_0 > the result you get is what you should expect. technically, the > vanishing forces on atoms are due to the vanishing ionic (Born) > effective charges, which in turn is due to the tetrahedral point > symmetry of atomic sites which is obviously wrong. (in binary semicondoctors the point symmetry of ionic sites is also tetrahedral, but the effective charges are obviously nonzero) in the diamond structure, vanishing effective charges results from dynamical charge neutrality [Z(1)+Z(2)=0], which says that the total force exerted by a uniform electric field on the crystal is zero, plus crystal symmetry, which requires Z(1)=Z(2). (here, of course, indeces (1) and (2) refer to the two lattice sites in the unit cell). again, sorry about that SB --- Stefano Baroni - SISSA & DEMOCRITOS National Simulation Center - Trieste http://www.sissa.it/~baroni / [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype) La morale est une logique de l'action comme la logique est une morale de la pens?e - Jean Piaget Please, if possible, don't send me MS Word or PowerPoint attachments Why? See: http://www.gnu.org/philosophy/no-word-attachments.html -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20080723/a46b9f10/attachment-0001.htm
