Dear Stefano, dear all. cell_dofree is useful when, for instance, you want to keep at least orthorombic a starting cubic cell, because you can force alpha, beta and gamma to be pi/2 (cell_dofree='xyz'). But there is no way (at least, no way that I'm aware of) to change all a, b and c and, at the same time, keep a=b=c. Suppose that you want to optimise a CoO rocksalt antiferromagnetic supercell: you need to differentiate the starting spin up and spin down Co atoms (Co1 and Co2). This lowers the symmetry, and the supercell becomes tetragonal along the simulation. I could provide further examples, and I think that a cell_dofree flag which allows one to retain the initial ibrav would be quite useful. I do not like to ask for things that I cannot implement by myself, but I may suggest that it could be a useful improvement...
Yours Giuseppe On Sunday 10 July 2011 23:20:08 Stefano de Gironcoli wrote: > If the symmetry is recognized vc-relax should keep it > if it is not there vc-relax cannot produce it unless the minimum the > system converges to has that symmetry. > there are codes (I recently discovered GULP) that can accept input > structure defined by the positions of the irreducible atoms + space > group definition... > pw.x does not have this capabiloity but if you generate the full list of > coordinates with one of such codes then pw.x should be able to recognize > the symmetry and keep it during relaxation. > > stefano > - > Stefano de Gironcoli - SISSA and DEMOCRITOS > > On 07/10/2011 09:09 PM, giuseppe.mattioli at mlib.ism.cnr.it wrote: > > Dear all > > I was thinking again about keeping the space group symmetry fixed > > along a vc-relax calculation. Actually, I did not directly ask my main > > question...:-) Is there a way to put the above constraint which I am > > not aware of? > > Yours > > > > Giuseppe > > > > ISM-CNR > > Italy > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum -- ******************************************************** - Article premier - Les hommes naissent et demeurent libres et ?gaux en droits. Les distinctions sociales ne peuvent ?tre fond?es que sur l'utilit? commune - Article 2 - Le but de toute association politique est la conservation des droits naturels et imprescriptibles de l'homme. Ces droits sont la libert?, la propri?t?, la s?ret? et la r?sistance ? l'oppression. ******************************************************** ? ?Giuseppe Mattioli ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?CNR - ISTITUTO DI STRUTTURA DELLA MATERIA ? ? ?v. Salaria Km 29,300 - C.P. 10 ? ? ? ? ? ? ? ? ? ?I 00015 - Monterotondo Stazione (RM) ? ? ? ? ? ? ?Tel + 39 06 90672836 - Fax +39 06 90672316 ? ? ? ?E-mail: <giuseppe.mattioli at ism.cnr.it>
