[Pw_forum] VC-relax collapsing unit cell

[Paolo Giannozzi]

I made a quick test with USPP's. The unit cell shrinks about 10%.

Paolo

On Tue, Nov 22, 2016 at 4:56 PM, John Bilgerman <bilgermanjohn at gmail.com>
wrote:

> Thanks for the tip. I'd only tried up to about a hundred in my tests, I'll
> start looking even higher. I attempted this over the weekend on my (old!)
> desktop, but found I will have to wait a week or two until I get cluster
> access before I can check and see if it was the only issue.
>
> Thanks,
> John
>
> On Sat, Nov 19, 2016 at 2:34 AM, Paolo Giannozzi <p.giannozzi at gmail.com>
> wrote:
>
>> Not sure this is the (only) problem, but 35 Ry for norm-conserving Iron
>> with semicore states is way too small. 200-300 Ry is a more appropriate
>> cutoff.
>>
>> Paolo
>>
>> On Sat, Nov 19, 2016 at 12:25 AM, 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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>>>
>>
>>
>>
>> --
>> 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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>>
>
>
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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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