On Sun, Oct 8, 2017 at 9:03 PM, Ricardo Afonso <rica...@df.ufscar.br> wrote:
> > Tsung-Lung Li explained the atoms will be moved independently according to > the forces acting on them. > if they are moved "according to the forces", they are not moved "independently", because the forces are constrained by the symmetry of the system. Paolo > And you said that is correct. It seems to me that somehow contradicts to > say that this still preserves the symmetry. > Please clarify if I'm wrong about this. Because I understand right to keep > the symmetry the atoms should be moved not only according to their forces, > but also preserving their coordinates, which suggests that their should > move isotropically, right? > > Thank you very much, > > Ricardo. > > On 5 October 2017 at 14:09, Paolo Giannozzi <p.gianno...@gmail.com> wrote: > >> On Thu, Oct 5, 2017 at 4:03 PM, Tsung-Lung Li <quan...@mail.ncyu.edu.tw> >> wrote: >> >> It seems to me QE does the following. >>> >>> 1. Initially, QE uses space_group and the 7 inequivalent atoms in >>> ATOMIC_POSITIONS to produce 24 atoms in the crystal unit cell. >>> >> >> correct >> >> >>> 2. In each subsequent geometric step of the 'relax' calculation, >>> the 24 atoms are moved independently according to the forces >>> acting on each atom. >>> >> >> correct >> >> >>> Therefore, at the end of the 'relax' calculation, the space_group=15 >>> symmetry is not always preserved. >>> >> >> not correct. Structural optimization based on forces does not break the >> symmetry, with occasional unfortunate exceptions due to numerical noise >> >> >>> Can QE only move the 7 inequivalent atoms and use space_group symmetry >>> to construct the other 17 atoms for next geometric step? >>> >> >> It could be done in principle, but it would require some extensive >> changes to the structural optimization algorithm, with dubious advantages >> in return. >> >> Paolo >> >> This way, the space_group symmetry will be preserved at the end of the >>> simulation. >>> >>> Thank you in advance. >>> >>> Best Regards, >>> Tsung-Lung Li >>> >>> ------------------------------------------------------------------ >>> &control >>> calculation = 'relax' >>> restart_mode = 'from_scratch' >>> / >>> &system >>> space_group = 15 >>> celldm(1) = 11.86181088389489 ! bohr >>> celldm(2) = 2.41851202803887 >>> celldm(3) = 0.903616377250279 >>> celldm(5) = -0.408489773780522 >>> ntyp = 4 >>> nat = 7 >>> / >>> >>> ATOMIC_SPECIES >>> Ca 40.0780000000 Ca_pbe_v1.uspp.F.UPF >>> S 32.0650000000 S_pbe_v1.2.uspp.F.UPF >>> O 15.9994000000 O.pbe-n-kjpaw_psl.0.1.UPF >>> H 1.0079000000 H.pbe-rrkjus_psl.0.1.UPF >>> >>> ATOMIC_POSITIONS crystal_sg >>> Ca 0.00000 0.17050 0.25000 >>> S 0.00000 0.32727 0.75000 >>> O 0.08319 0.27218 0.59103 >>> O 0.19997 0.38195 0.91298 >>> O -0.20823 0.06826 -0.07831 >>> H -0.25800 0.08700 -0.23400 >>> H -0.24400 0.02000 -0.07700 >>> >>> _______________________________________________ >>> Pw_forum mailing list >>> Pw_forum@pwscf.org >>> http://pwscf.org/mailman/listinfo/pw_forum >> >> >> >> -- >> Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche, >> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy >> Phone +39-0432-558216 <+39%200432%20558216>, fax +39-0432-558222 >> <+39%200432%20558222> >> >> >> _______________________________________________ >> Pw_forum mailing list >> Pw_forum@pwscf.org >> http://pwscf.org/mailman/listinfo/pw_forum >> > > > > -- > Ricardo Afonso > Student of Magnetism and Superconductivity Group > Federal University of Sao Carlos > > _______________________________________________ > Pw_forum mailing list > Pw_forum@pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum > -- Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche, Univ. Udine, via delle Scienze 208, 33100 Udine, Italy Phone +39-0432-558216, fax +39-0432-558222
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