Paolo, Thanks for your reply. I was not aware of the option "cell_dofree". However, the options there may not completely cover all possible situations. In general, I would like to constrain the upper triangle of the cell_parameters matrix to zero (perhaps as a default), and this does not seem available. In another case, when working with surface slabs, I would like to vary v1_x, v2x and v2y, while keeping v3z constrained to a nonzero value and all the rest of the elements constrained to zero. In general, an additional control to what is available already in "cell_dofree" could be very useful by following the convention already used for constraining the Cartesian atomic positions, just adding 3 optional numbers (0-s or 1-s) at the end of the lines of the cell_parameter matrix. Anyway, I am a very frequent user of Quantum Espresso and I greatly appreciate the high quality of code you have developed.
Best regards: Karoly http://science.iit.edu/people/faculty/karoly-nemeth ________________________________________ From: Paolo Giannozzi [[email protected]] Sent: Sunday, March 16, 2014 8:39 AM To: PWSCF Forum Cc: Nemeth, Karoly Subject: Re: [Pw_forum] constraining Cartesian lattice vector components Have you looked at option "cell_dofree"? P. On Sun, 2014-03-16 at 01:41 +0000, Nemeth, Karoly wrote: > Dear Quantum Espresso developers and users, > > I was wondering whether it is possible to constrain individual Cartesian > components of the lattice vectors during geometry optimization (vc-relax), at > least for the ibrav=0 case. This would in principle be similar to > constraining Cartesian atomic positions, however, it appears that this > feature is not available in Quantum Espresso yet. > > Also, it appears that during vc-relax the cell is slightly rotated. I would > expect that the first two lattice vectors remain along the x axis and in the > xy plane while the third one may have non-zero x, y and z components. In > other words, if I start the optimization with the upper triangle of the > cell_parameters matrix being all zero, I would expect that it stays so, and > only the diagonals and the lower triangle will vary, which includes 6 numbers > only. These six non-zero numbers represent the 6 lattice parameters in > Cartesian space. Allowing all 9 numbers to vary in the cell_parameters matrix > introduces redundancy that may lead to the rotation of the cell and slows > down convergence. > > I would greatly appreciate any advice in the above two (related) matters. > > Thanks: > > Karoly > http://science.iit.edu/people/faculty/karoly-nemeth > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum -- Paolo Giannozzi, Dept. Chemistry&Physics&Environment, Univ. Udine, via delle Scienze 208, 33100 Udine, Italy Phone +39-0432-558216, fax +39-0432-558222
