[QE-users] Monoclinic structure optimization

[Luiz Gustavo Davanse da Silveira]

Dear Malte,

Thank you for your advice. The calculation with degauss = 0.01 had some
convergence problems but the one with degauss = 0.005 worked just fine.
Just for the record, mixing_beta had to be reduced to 0.3 to achieve
convergence.

By the way, I don't have much experience on simulating metals, therefore,
I have many doubts on how to choose the appropriate smearing method and
degauss value. I constructed a total energy vs degauss value curve but the
overall behavior didn't tell me much. Anyway, could you point me to the
right direction on how to choose these parameters? Or could you suggest me
some resources that I can use to learn more about it?

Regards,
Luiz Gustavo D. Silveira
UFPR - Brazil


Em Ter, Junho 16, 2020 12:59 pm, Malte Sachs escreveu:
> Dear Luiz,
>
>
> from my experience you are using a quite high degauss value of 0.06 for a
> metal. I would guess that for TiNi this value is crucial for the
> distortion. I would try to reduce it to about 0.01 or even 0.005 Ry.
> Moreover, I would recommend to use a marzari-vanderbilt smearing
> compared to the simple gaussian you are using. And as a guess, I think you
> can start your optimization with lower cutoff values (e.g. ecutwfc = 70 Ry
> and ecutrho = 560 Ry). This was a safe choice for similar systems I have
> investigated (with the same pseudos).
>
> Best regards,
> Maltem
>
>
> Am 16.06.20 um 17:12 schrieb Luiz Gustavo Davanse da Silveira:
>
>> Dear QE users,
>>
>>
>> I am trying to optimize NiTi (nitinol) martensite structure
>> (monoclinic,
>> space group P21/m) via a vc-relax calculation with cell_dofree = 'ibrav'
>>  option. The problem is that QE gives me a gamma angle of almost 90°
>> while the experimental value is around 97°. I tried to construct an
>> energy vs gamma curve keeping the angle fixed and relaxing the axis with
>> cell_dofree = 'volume' but it doesn't work since the axis are not
>> orthogonal. I don't know what else I can try. If anyone could give me a
>> hint it will be very much appreciated.
>>
>> Find below my input file and the final coordinates outputed by QE.
>>
>>
>> &CONTROL
>> calculation = 'vc-relax' outdir = './outdir' prefix = 'niti' etot_conv_thr
>> = 1.0E-4
>> pseudo_dir = './pseudo' disk_io = 'none' /
>> &SYSTEM
>> ibrav = 12 A = 2.8
>> B = 4.5
>> C = 4
>> cosAB = -0.1184 nat = 4 ntyp = 2 ecutwfc = 110 ecutrho = 1760
occupations =
>> 'smearing'
>> degauss = 0.06 smearing = 'gauss' /
>> &ELECTRONS
>> conv_thr = 1.E-8 /
>> &IONS
>> /
>> &CELL
>> cell_dofree = 'ibrav' /
>> ATOMIC_SPECIES
>> Ni 58.6934 Ni.pbesol-spn-kjpaw_psl.1.0.0.UPF
>> Ti 47.867 Ti.pbesol-spn-kjpaw_psl.1.0.0.UPF
>> ATOMIC_POSITIONS {crystal}
>> Ni 0.9475 0.8070 0.25
>> Ni 0.0525 0.1930 0.75
>> Ti 0.5274 0.2790 0.25
>> Ti 0.4726 0.7210 0.75
>> K_POINTS {automatic}
>> 14 9 10 0 0 0
>>
>>
>>
>>
>> CELL_PARAMETERS (alat=  5.29123317)
>> 1.002403137   0.000000000   0.000000000
>> -0.005714828   1.587445555   0.000000000
>> 0.000000000   0.000000000   1.513222861
>>
>>
>> ATOMIC_POSITIONS (crystal)
>> Ni            0.9995289657        0.8063481974        0.2500000000
>> Ni            0.0004710343        0.1936518026        0.7500000000
>> Ti            0.5020451582        0.2794391874        0.2500000000
>> Ti            0.4979548418        0.7205608126        0.7500000000
>>
>>
>>
>>
>> Best regards,
>> Luiz Gustavo D. Silveira
>> UFPR - Brazil
>>
>>
>> _______________________________________________
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>>
>
>
> --
> Malte Sachs
> Anorganische Chemie, Fluorchemie
> Philipps-Universität Marburg
> Hans-Meerwein-Straße 4
> 35032 Marburg (Paketpost: 35043 Marburg)
> Tel.: +49 (0)6421 28 - 25 68 0
> http://www.uni-marburg.de/fb15/ag-kraus/
>
>
>
>