[Pw_forum] Problem with determination of U using linear response
Matteo Cococcioni
matteo at umn.edu
Wed May 27 14:04:50 CEST 2015
Dear Prasenjit,
I do not know the answer to your question (it probably depends on the
details of the DOS of your system) but the situation does not look tragic
to me.
I guess you can always expect a departure from linearity when the
perturbation grows bigger. typically I use values within -0.1 and 0.1.
Why the interacting response is more well behaved than the other? I am not
sure. maybe it's because the screenening lowers the effective magnitude of
the perturbation and so it's like you have been using a smaller alpha.
Hope this helps,
Matteo
On Wed, May 27, 2015 at 9:13 AM, Prasenjit Ghosh <prasenjit.jnc at gmail.com>
wrote:
> Dear all,
>
> I am using linear response to determine U for Fe. In my system, there are
> two types of Fe atom, one in which the Fe is in an O octahedron and the
> second in which it is in an O terahedron.
> When I am plotting the occupation number of the Fe d as a function of
> perturbation alpha (-0.2 .le. alpha .le 0.2), for the non interacting
> electron system, I am not getting a linear plot for the whole range of
> alpha while for the interacting one it remains linear.
> For example when Fe is in the O octahedra, the response does not remain
> linear for alpha is greater than 0.05 or less than -0.05. However, for the
> interacting case, it remains linear for the whole regime (please refer to
> the attached plot for Fe in O octahedra).
> Further for this case for alpha=0, the occupation for the interacting and
> non interacting ones are not exactly same. While for the non-interacting
> one the occupation is 6.60012, it is 6.60162 for the interacting one.
>
> Similarly for the tethedra, for alpha=-0.2, the non-interacting response
> does not remain linear while for the interacting one it remains linear.
>
> I was wondering whether one has faced similar situations and if so can
> provide me some hints as to what might be the probable reason for the same?
>
> Below is the input file I am using for the calculation:
>
> for alpha in -0.20 -0.15 -0.10 -0.05 0.00 0.05 0.10 0.15 0.20
>
> do
>
> mkdir /scratch/pghosh/octfe/alpha$alpha
>
> cd /scratch/pghosh/octfe/alpha$alpha
>
> ethr=`grep ethr /home/pghosh/Ca2Fe2O5/octfe/scf.out | tail -1 | awk
> '{print $3}'`
>
> rm -rf Ca2Fe2O5-noU-vcrel-AFM.*
>
> cp -r ../Ca2Fe2O5-noU-vcrel-AFM.* .
>
> cat > scf-octFe.$alpha.in << EOF
> &control
> calculation = 'scf',
> prefix = 'Ca2Fe2O5-noU-vcrel-AFM',
> outdir = '/scratch/pghosh/octfe/alpha$alpha'
> pseudo_dir = '/home/pghosh/pseudo'
> /
> &system
> ibrav = 0,
> celldm(1)=10.25176385
> nat = 36,
> ntyp = 5,
> ecutwfc = 45
> ecutrho = 320
> nspin=2
> starting_magnetization(2)=-1.0
> starting_magnetization(3)=1.0
> starting_magnetization(4)=-1.0
> occupations='smearing'
> degauss=0.001
> smearing='gaussian'
> lda_plus_u = .true.,
> U_projection_type = 'atomic',
> Hubbard_U(2) = 1.d-10
> Hubbard_U(3) = 1.d-10
> Hubbard_U(4) = 1.d-10
> Hubbard_U(5) = 1.d-10
> Hubbard_alpha(4) = $alpha
> /
> &electrons
> mixing_beta = 0.3
> conv_thr = 1.0d-8,
> startingwfc = 'file',
> startingpot = 'file',
> diago_thr_init = $ethr
> /
>
> ATOMIC_SPECIES
> Ca 87.62 Ca.pw91-nsp-van.UPF
> Fe1 47.867 Fe.pw91-sp-van_ak.UPF
> Fe2 47.867 Fe.pw91-sp-van_ak.UPF
> Fe3 47.867 Fe.pw91-sp-van_ak.UPF
> O 15.999 O.pw91-van_ak.UPF
> ATOMIC_POSITIONS (crystal)
> Ca 0.479439516 0.108738866 0.023376810
> Ca 0.979439516 0.391261134 0.476623190
> Ca 0.520560484 0.608738866 0.976623190
> Ca 0.020560484 0.891261134 0.523376810
> Ca 0.520560484 0.891261134 0.976623190
> Ca 0.020560484 0.608738866 0.523376810
> Ca 0.479439516 0.391261134 0.023376810
> Ca 0.979439516 0.108738866 0.476623190
> Fe3 0.000000000 0.000000000 -0.000000000
> Fe1 0.500000000 0.500000000 0.500000000
> Fe1 0.000000000 0.500000000 -0.000000000
> Fe1 0.500000000 -0.000000000 0.500000000
> Fe2 0.948517158 0.250000000 0.935170308
> Fe2 0.448517158 0.250000000 0.564829692
> Fe2 0.051482842 0.750000000 0.064829692
> Fe2 0.551482842 0.750000000 0.435170308
> O 0.262959232 0.985181682 0.237331409
> O 0.762959232 0.514818318 0.262668591
> O 0.737040768 0.485181682 0.762668591
> O 0.237040768 0.014818318 0.737331409
> O 0.737040768 0.014818318 0.762668591
> O 0.237040768 0.485181682 0.737331409
> O 0.262959232 0.514818318 0.237331409
> O 0.762959232 0.985181682 0.262668591
> O 0.027189198 0.140319152 0.069344138
> O 0.527189198 0.359680848 0.430655862
> O 0.972810802 0.640319152 0.930655862
> O 0.472810802 0.859680848 0.569344138
> O 0.972810802 0.859680848 0.930655862
> O 0.472810802 0.640319152 0.569344138
> O 0.027189198 0.359680848 0.069344138
> O 0.527189198 0.140319152 0.430655862
> O 0.586951586 0.250000000 0.888451999
> O 0.086951586 0.250000000 0.611548001
> O 0.413048414 0.750000000 0.111548001
> O 0.913048414 0.750000000 0.388451999
> K_POINTS (automatic)
> 9 3 9 1 1 1
> CELL_PARAMETERS (alat)
> 0.991167212 0.000000000 0.000000000
> 0.000000000 2.746908521 0.000000000
> 0.000000000 0.000000000 1.023657125
> EOF
>
>
>
> With regards,
>
> Prasenjit
> --
> PRASENJIT GHOSH,
> IISER Pune,
> Dr. Homi Bhabha Road, Pashan
> Pune, Maharashtra 411008, India
>
> Phone: +91 (20) 2590 8203
> Fax: +91 (20) 2589 9790
>
> _______________________________________________
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> Pw_forum at pwscf.org
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>
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