[Pw_forum] Run QE with space_group and "ATOMIC_POSITIONS crystal_sg"

[Ilya Ryabinkin]

Paolo:
I'm sorry for intercepting you discussion, but... You are saying that
forces always belong to the totally symmetric rep of a given group.
Would it be possible, however, for some complicated electronic
structure that KS solutions exhibit lower symmetry than the
corresponding Hamiltonian? In quantum chemistry of molecules such a
situation occasionally takes place and is called "spontaneous symmetry
breaking".

Thanks of the reply,
Ilya

On Sun, Oct 8, 2017 at 3:24 PM, Paolo Giannozzi <p.giannozzi at gmail.com> wrote:
> On Sun, Oct 8, 2017 at 9:03 PM, Ricardo Afonso <ricardo at 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.giannozzi at gmail.com> wrote:
>>>
>>> On Thu, Oct 5, 2017 at 4:03 PM, Tsung-Lung Li <quantum at 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
>>>>
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>>>
>>>
>>>
>>> --
>>> 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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>>
>>
>>
>>
>> --
>> Ricardo Afonso
>> Student of Magnetism and Superconductivity Group
>> Federal University of Sao Carlos
>>
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>
>
>
>
> --
> 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
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-- 
*******************************************************
                    Ilya Ryabinkin
                 Postdoctoral Scholar
          Physical and Environmental Sciences
           University of Toronto Scarborough
  http://www.utsc.utoronto.ca/~aizmaylov/Members.html
*******************************************************