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 <[email protected]> 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 > > _______________________________________________ > Pw_forum mailing list > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum >
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