On Sep 17, 2006, at 3:13 PM, hailin yu wrote: > Dear all: > I have some questions about the phonon calculation of Pt. > 1). Is it reasonable to calculate the phonon dispersion of Pt > by using the Pt.pbe-rrkjus.UPF pseudopotentials?
why not? > 2). For the value of degauss, how it is reasonable? And for > the kpoint? Only you can tell. This is not so difficult to assess. Take a few representative points in the BZ and calculate the phonon frequencies as functions of degauss. For each value of degauss, keep increasing the number of k points until you reach convergence. Note: (1) the resulting number of k-pts should increase with decreasing degauss; (2) this is the order to follow (i.e. degauss first, convergence wrt to k-points for each given value of degauss: not the other way around). Finally choose the value of degauss (and the corresponding number of k-pts) which gives you the accuracy you desire. In normal circumstances, such as Pt, I would say, the optimal value of degauss should not depend on the phonon wavevector. At a Kohn anomaly, instead, a much smaller degauss (and a correspondingly larger number of k-pts) than at "ordinary" phonon wave-vectors is usually needed. Can you see why? (if you understand this you understand a lot of the fine details of phonon calculations in metals). Take care Stefano --- Stefano Baroni - SISSA & DEMOCRITOS National Simulation Center - Trieste [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype) 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: /pipermail/attachments/20060917/e3be13db/attachment.htm
