[Pw_forum] equilibrium lattice constant of magnetite

[Jia Chen]

Hi,

You need to figure out numbers of each atomic specie and positions of each
atom, ibrav = 2 only gives you three fcc lattice vectors. I don't think it
implies fd3m space group.

Bests
Jia

On Mon, Aug 6, 2012 at 10:42 AM, Abolore Musari <abmus007 at gmail.com> wrote:

> Thanks so much Jia
> But Sir the atomic positions in the input is for 3 atoms, should l leave
> the atomic position and change the number of atom or my atomic position is
> wrong??
> thanks
> Musari A. A
> UNAAB Nigeria
>
>
> On Mon, Aug 6, 2012 at 3:34 PM, jia chen <jiachen at princeton.edu> wrote:
>
>> Dear Abolore Musari,
>>
>> I guess the number of atoms should be 14, instead of 3.
>>
>> Regards
>> Jia
>>
>> On Mon, Aug 6, 2012 at 10:24 AM, Abolore Musari <abmus007 at gmail.com>wrote:
>>
>>> Dear QE users
>>> Sir, I am try to find the lattice constant of magnetite (Fe3O4) which is
>>> a spinel ferrimagnetic material. The expt lattice constant was 15.87 and I
>>> have been trying to find the equilibrium lattice constant (celldm(1))
>>> between 15.80 - 16.00 and all i get is a straight line graph instead of the
>>> usual exponential curve graph. I have tried all l could most esp with
>>> starting_magnetization but the results are the same. My input is pasted
>>> below pls help me to get the appropriate graph.
>>> The kind of the graph I got is attached.
>>> Thanks
>>>
>>> &control
>>>     calculation = 'scf',
>>>     restart_mode ='from_scratch',
>>>     prefix = 'Fe3O4',
>>>     pseudo_dir = '/home/abolore/Programs/Pseudos/',
>>>     outdir = './tmp/'
>>>  /
>>>  &system
>>>     ibrav = 2,
>>>     celldm(1)= $15.80-16.00,
>>>     nat = 3,
>>>     ntyp = 3,
>>>     ecutwfc = 40,
>>>     ecutrho = 400,
>>>     starting_magnetization(1) = 0.7,
>>>     starting_magnetization(2) = -0.5,
>>>     starting_magnetization(3) = 0.0,
>>>     nspin = 2,
>>>     occupations='smearing',
>>>     smearing='gaussian',
>>>     degauss = 0.05,
>>>  /
>>>  &electrons
>>>    diagonalization = 'david',
>>>    mixing_mode = 'plain',
>>>    mixing_beta = 0.7
>>>  /
>>> ATOMIC_SPECIES
>>>     Fe1     55.845   Fe.pz-nd-rrkjus.UPF
>>>     Fe2     55.845      Fe.pz-nd-rrkjus.UPF
>>>      O      16.000      O.pz-rrkjus.UPF
>>>
>>> ATOMIC_POSITIONS
>>> Fe1 0.125  0.125  0.125
>>> Fe2 0.500  0.500  0.500
>>> O    0.2548 0.2548 0.2548
>>>
>>> K_POINTS (automatic)
>>>   8 8 8 1 1 1
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
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>>>
>>
>>
>> --
>> Jia Chen
>>
>>
>>
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>
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-- 
Jia Chen

Dept of Chemistry
Princeton University
Princeton, NJ 08544
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