Oh now it is clear to me. Thank you very much for your reply.
On 8 October 2017 at 16:24, Paolo Giannozzi <[email protected]> wrote: > On Sun, Oct 8, 2017 at 9:03 PM, Ricardo Afonso <[email protected]> > 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 <[email protected]> >> wrote: >> >>> On Thu, Oct 5, 2017 at 4:03 PM, Tsung-Lung Li <[email protected]> >>> 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 >>>> [email protected] >>>> 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 >>> [email protected] >>> http://pwscf.org/mailman/listinfo/pw_forum >>> >> >> >> >> -- >> Ricardo Afonso >> Student of Magnetism and Superconductivity Group >> Federal University of Sao Carlos >> >> _______________________________________________ >> Pw_forum mailing list >> [email protected] >> 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 > > > _______________________________________________ > Pw_forum mailing list > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum > -- Ricardo Afonso Student of Magnetism and Superconductivity Group Federal University of Sao Carlos
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