The energy of charged cells depends upon a rather arbitrary choice of the G=0 potential. If you compare the energies from CP with those from PW, you will notice that they are quite the same (once the factor 2 between Ry and Ha is taken into account!) for neutral cells, while they differ for charged cells: CP uses a different convention for G=0. In principle, forces and stresses might also depend upon the choice of the G=0. I have never felt or heard that this effect is in practice relevant for structural optimization. I am less sure about variable-cell optimization, though
Paolo On Fri, Apr 30, 2021 at 4:11 PM Hanghui Chen <chenhanghuipw...@gmail.com> wrote: > Dear QE developers, > I have been using Quantum Espresso for more than a decade and > recently a paper (PRB 91, 024107 (2015)) caught my attention, which shows > that the total energy, pressure and cell relaxation are ill-defined in > charged systems (even if a compensating charge background is present). The > paper shows that the total energy and pressure of a charged system depend > on the average electrostatic potential convention, and thus is > code-dependent (QE, ABINIT and VASP use different conventions). > I think the paper is theoretically correct. However in practice, we > have recently tested doped ferroelectric materials using both QE and VASP. > In this charged system, we find both QE and VASP yield qualitatively > consistent structural properties. > Since relaxation of a charged system is very common in literature > using QE or VASP (e.g. PRL 109, 247601 (2012) and many others), I am > wondering whether the relaxed structure of a charged system from QE is > reliable. According to PRB 91, 024107, it is not legitimate to do cell > relaxation of a charged system. However both QE and VASP do allow to > calculate total energy and perform cell relaxation in a charged system. And > from literature, it seems that the relaxed structure of a charge system > from QE or VASP calculations is "not too wrong". > So what is your insight on this issue? Shall we prohibit ourselves > from doing cell relaxation of a charged system in QE, or can we still use > the standard procedure but with the caution that the optimized structure of > a charged system from QE might not be accurate (due to the QE convention of > average electrostatic potential)? > Thank you very much. > > Dr. Hanghui Chen > Department of Physics > NYU Shanghai and New York University > > _______________________________________________ > Quantum ESPRESSO is supported by MaX (www.max-centre.eu) > users mailing list users@lists.quantum-espresso.org > https://lists.quantum-espresso.org/mailman/listinfo/users -- Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche, Univ. Udine, via delle Scienze 206, 33100 Udine, Italy Phone +39-0432-558216, fax +39-0432-558222
_______________________________________________ Quantum ESPRESSO is supported by MaX (www.max-centre.eu) users mailing list users@lists.quantum-espresso.org https://lists.quantum-espresso.org/mailman/listinfo/users
