[Pw_forum] VC-relax collapsing unit cell

[Stefano de Gironcoli]

I dont know if this is the problem but the last two oxygens are 4c not 8d

stefano 
(sent from my phone)

> On 19 Nov 2016, at 00:25, John Bilgerman <bilgermanjohn at gmail.com> wrote:
> 
> Hi,
> 
> I've been banging my head against this and cannot find what is likely a silly mistake despite many tests and lots of reading.
> 
> I'm trying to optimize the (known) structure of NaFePO4 as a test. I'm starting from the experimental crystal structure, so the drastic collapse of the unit cell to < 1/2 suggests an issue.
> 
> I know the common problem is inputing the structure wrong, but I've done my best (and sanity-checked the input/output files with Xcrysden).
> 
> I'm new to QE, any help would be appreciated.
> 
> Input file:
>  &CONTROL
>                  calculation = 'vc-relax' ,
>                 restart_mode = 'from_scratch' ,
>                       outdir = './' ,
>                       wfcdir = './scratch' ,
>                   pseudo_dir = './pseudo' ,
>                      disk_io = 'default' ,
>                    verbosity = 'high' ,
>  /
>  &SYSTEM
>                        ibrav = 8,
>                  space_group = 62 ,
>                            A = 9.001 ,
>                            B = 6.874 ,
>                            C = 5.052 ,
>                        cosAB = 0 ,
>                        cosAC = 0 ,
>                        cosBC = 0 ,
>                          nat = 6,
>                         ntyp = 4,
>                      ecutwfc = 35 ,
>                      ecutrho = 140 ,
>                  occupations = 'smearing' ,
>                      degauss = 0.02 ,
>                     smearing = 'gaussian' ,
>                        nspin = 2 ,
>    starting_magnetization(1) = 0.7,
>    starting_magnetization(2) = 0,
>    starting_magnetization(3) = 0,
>    starting_magnetization(4) = 0,
>                     noncolin = .false. ,
>  /
>  &ELECTRONS
>              diagonalization = 'david' ,
>  /
>  &IONS
>  /
>  &CELL
>  /
> ATOMIC_SPECIES
>    Fe   55.00000  Fe.pbe-sp-hgh.upf 
>     P   30.00000  P.pbe-hgh.upf 
>    Na   22.00000  Na.pbe-sp-hgh.upf 
>     O   16.00000  O.pbe-hgh.upf 
> ATOMIC_POSITIONS crystal_sg 
> Fe 4a 
> P 4c 0.17585  0.46447
> Na 4c  0.34999  0.9702
> O 8d 0.1212 0.0682 0.3177
> O 8d 0.3486 0.25 0.4561
> O 8d 0.1154 0.25 0.7507
> K_POINTS automatic 
>   2 3 4   1 1 1 
> 
> 
> The relevant parts of the CIF file for the structure are:
> ...
> _cell_length_a 9.001(8)
> _cell_length_b 6.874(3)
> _cell_length_c 5.052(4)
> _cell_angle_alpha 90.
> _cell_angle_beta 90.
> _cell_angle_gamma 90.
> _cell_volume 312.58
> _cell_formula_units_Z 4
> _symmetry_space_group_name_H-M 'P n m a'
> _symmetry_Int_Tables_number 62
> ...
> Fe1 Fe2+ 4 a 0 0 0 . 1. 0
> P1 P5+ 4 c 0.17585(4) 0.25 0.46447(8) . 1. 0
> Na1 Na1+ 4 c 0.34999(9) 0.25 0.9702(2) . 1. 0
> O1 O2- 8 d 0.1212(1) 0.0682(1) 0.3177(2) . 1. 0
> O2 O2- 4 c 0.3486(1) 0.25 0.4561(2) . 1. 0
> O3 O2- 4 c 0.1154(1) 0.25 0.7507(2) . 1. 0
> ...
> 
> John
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