[QE-users] ibrav number check

[Yunzhe Wang]

The atomic positions you gave are not precise enough. Some symmetrical equivalent positions are determined as asymmetrical since internally, only positions matched up to 10^-5 are considered as equivalent.

As you can imagine, if you put a basis with lower symmetry, then some symmetries of the lattice will be broken.

Best,
Yunzhe Wang
Mueller Research Group,
Johns Hopkins University


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________________________________
From: users <users-bounces at lists.quantum-espresso.org> on behalf of Giovanni Cantele <giovanni.cantele at spin.cnr.it>
Sent: Monday, November 19, 2018 5:02 PM
To: Quantum Espresso users Forum
Subject: Re: [QE-users] ibrav number check

maybe you’re visualising the conventional, rather than the primitive unit cell.
Try to set Display -> Primitive Cell Mode

The bct unit cel should show up.

Giovanni

--

Giovanni Cantele, PhD

CNR-SPIN
c/o Dipartimento di Fisica
Universita' di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
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e-mail: giovanni.cantele at spin.cnr.it<mailto:giovanni.cantele at spin.cnr.it>
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On 19 Nov 2018, at 19:38, Chan, Edmund <thc208 at exeter.ac.uk<mailto:thc208 at exeter.ac.uk>> wrote:

Dear all users,

I am currently trying to relax a methylammonium lead iodide CH3NH3PbI3 structure which has tetragonal structure I4/mcm. Thus, in my input file, I select ibrav = 7 (body centred teragonal). However, as I visualise the input and output on Xcrysden, the unit cell becomes orthorhombic. Why is that?


&CONTROL
                       title = 'MAPI' ,
                 calculation = 'relax' ,
                restart_mode = 'from_scratch' ,
                      outdir = './' ,
                  pseudo_dir = './' ,
                      prefix = 'CH3NH3PbI3' ,
/
&SYSTEM
                       ibrav = 7,
                   A = 8.83920,
                   C = 12.6948,
                         nat = 12,
                        ntyp = 5,
                     ecutwfc = 80 ,
                       ecutrho = 800,
/
&ELECTRONS
            electron_maxstep = 5000 ,
                    conv_thr = 1.0d-6 ,
                 mixing_beta = 0.3 ,
/
&IONS
                ion_dynamics = 'bfgs' ,
/
ATOMIC_SPECIES
    C   12.01070  c_pbesol_v1.2.uspp.F.UPF
    H    1.00794  H.pbesol-rrkjus_psl.0.1.UPF
    N   14.00670  N.pbesol-theos.UPF
   Pb  207.20000  Pb.pbesol-dn-kjpaw_psl.0.2.2.UPF
    I  126.90450  i_pbesol_v1.uspp.F.UPF
ATOMIC_POSITIONS alat
   Pb      0.000000000    0.000000000    0.500000000
    I      0.000000000    0.000000000    0.250000000
    I      0.294200000    0.205800000    0.500000000
    I     -0.294200000   -0.207600000    0.500000000
    C      0.544000000    0.921000000    0.784000000
    H      0.609200000    1.002100000    0.769900000
    H      0.557300000    0.845500000    0.724600000
    H      0.551500000    0.875200000    0.864300000
    N      0.389000000    0.987000000    0.767000000
    H      0.324700000    0.913900000    0.730300000
    H      0.381400000    1.068100000    0.734300000
    H      0.339300000    0.990800000    0.831000000
K_POINTS automatic
  1 1 1   0 0 0

Thank you all.


Kind regards,

Edmund Chan
________________________________________________
Edmund Chan
PhD Renewable Energy Student
Environment & Sustainablity Institute
College of Engineering, Mathematics and Physical Sciences
University of Exeter, Penryn Campus
Penryn, Cornwall
United Kingdom
TR10 9FE

Tel: +44 (0)7455 235 701<tel:+44%207455%20235%20701>
Email: thc208 at exeter.ac.uk<mailto:thc208 at exeter.ac.uk>
LinkedIn: https://uk.linkedin.com/in/edmundchan1
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