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 Get Outlook for iOS<https://aka.ms/o0ukef> ________________________________ From: users <users-boun...@lists.quantum-espresso.org> on behalf of Giovanni Cantele <giovanni.cant...@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 Via Cintia, I-80126, Napoli, Italy e-mail: giovanni.cant...@spin.cnr.it<mailto:giovanni.cant...@spin.cnr.it> gcant...@gmail.com<mailto:gcant...@gmail.com> Phone: +39 081 676910 Skype contact: giocan74 Web page: https://sites.google.com/view/giovanni-cantele On 19 Nov 2018, at 19:38, Chan, Edmund <thc...@exeter.ac.uk<mailto:thc...@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: thc...@exeter.ac.uk<mailto:thc...@exeter.ac.uk> LinkedIn: https://uk.linkedin.com/in/edmundchan1 <image002.jpg> <image003.gif> _______________________________________________ users mailing list users@lists.quantum-espresso.org<mailto:users@lists.quantum-espresso.org> https://lists.quantum-espresso.org/mailman/listinfo/users
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