On Thursday 05 January 2006 16:28, Lilia Boeri wrote: > I was wondering whether it is possible with PWSCF to optimize the unit > cell while keeping the internal degrees of freedom (i.e. the reduced > coordinates in the unit cell) fixed.
you may try to set the force on atoms to 0: in variable-cell dynamics, atomic positions are automatically scaled with the crystal axis. Not sure at all it will work, and even less that it will do what you hope for. > if I have, for example, an hexagonal system and I want to find how the c/a > ratio evolves with pressure, I suppose I should calculate, for different > volumes, the total energy as a function of c/a keeping the volume fixed. > Then I would take the minimum point for each volume and with this build > a E(V) curve, differentiate and calculate the P(V) curve. > [...] is the above procedure correct? I hope so: this is how I calculated the equilibrium lattice parameter of MgB_2, once upon a time... see attached script and fortran code. And yes, at equilibrium the stress is isotropic (it should be 0 but its diagonal part, i.e. the pressure, won't be 0 until you go to very high cutoffs) Paolo -- Paolo Giannozzi e-mail: giannozz at nest.sns.it Scuola Normale Superiore Phone: +39/050-509876, Fax:-563513 Piazza dei Cavalieri 7 I-56126 Pisa, Italy -------------- next part -------------- A non-text attachment was scrubbed... Name: mgb2.j Type: application/x-shellscript Size: 1356 bytes Desc: not available Url : /pipermail/attachments/20060113/798a24d6/attachment.bin -------------- next part -------------- A non-text attachment was scrubbed... Name: minsq.f Type: text/x-fortran Size: 1233 bytes Desc: not available Url : /pipermail/attachments/20060113/798a24d6/attachment-0001.bin
