Hi Yang, I had the experience to work with twinning in P212121space group. My crystals belong to space group P212121with unit cell dimensions a=82.39, b=123.92 and c=128.89A. You can see that"b" and "c" are not equal but very simmilar, and this factcan allow twinning for this space group. The crystals with higher fraction oftwinning can be easier processed in tetragonal space group P41212with unit cell dimensions a=b=126.95 and c=82.43A.However the packing is actually orthorhombic. In my work, to fully assessthe twin fraction and the twin operator was employed the program PHENIX(xtriage tool). I solvedmy crystal structure using data suggested by PHENIX program (twin operator (-h,-l,-k)).
Goodluck! Matheus On Mon, 21 Jun 2010 13:52:05 -0700, yang li wrote > Dear all, > > Is there any possible of twining for a normal P212121 spacegroup and > what is the twin law, say no equal cell dimensions? > Some people said there is no twin law for such symmetry but I am not very > sure. Thanks a lot. > > Best > Yang ------------------------------------------------------------- Matheus Pinto Pinheiro Laboratório de Cristalografia de Proteínas Departamento de Física e Química Faculdade de Ciências Farmacêuticas de Ribeirão Preto - USP Brasil Fone: +55.16.3602.4193 m...@fcfrp.usp.br
