Yes, I am using CRYSTAL coordinates. 3/4 1/4 3/4 and 1/4 1/4 1/4 differs in a 1/2 0 1/2 translation and then they are equivalent in a F-centered cell. In fact 0 0 0 and 3/4 1/4 3/4 are the coordinates for the position 8a in International Tables of Crystallography!!
Best wishes, Miguel -----Mensaje original----- De: pw_forum-admin at pwscf.org [mailto:pw_forum-admin at pwscf.org] En nombre de degironc Enviado el: martes, 23 de mayo de 2006 19:44 Para: pw_forum at pwscf.org Asunto: Re: [Pw_forum] symmetry operations Are you using CRYSTAL coordinates? in this case 3/4 1/4 3/4 and 1/4 1/4 1/4 are NOT equivalent. the former is wrong and corrseponds to the following cartesian coordinates (from the PWscf output) 2 Si tau( 2) = ( -0.7500000 0.5000000 0.5000000 ) which are obviously wrong. stefano Miguel A. Salvad? wrote: > > > Dear PWusers: > > > > I do not understand how PWSCF generate the symmetry operations from > ibrav and crystal coordinates. > > A simple example: C diamond (Fd-3m) with C at 8a (0,0,0) (Cell choice 1). > > If I run a calculation with ibrav 2 (cubic F-centered) and two C atoms > at 0,0,0 and 3/4,1/4,3/4 the program found 16 symmetry operations. > > But if I change the second position to the equivalent one 1/4 1/4 1/4, > then the program found successfully 48 symmetry operations. > > I have found this problem with more complex structures and it is not > easy to check all the possibilities of equivalent positions combinations. > > Any kind of help will be welcome, > > Best wishes, > > > > Miguel A. Salvad? > > > > > > Miguel A. Salvad? > > Dpto. Quimica Fisica y Analitica > > Universidad de Oviedo > > Spain > > E-mail: mass at uniovi.es > > > > > > > _______________________________________________ Pw_forum mailing list Pw_forum at pwscf.org http://www.democritos.it/mailman/listinfo/pw_forum
