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, fax +39-0432-558222
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