<div dir="ltr"><div>Dear Prasenjit,<br><br></div><div>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.<br></div><div>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.<br></div><div>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.<br><br></div><div>Hope this helps,<br><br></div><div>Matteo<br></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, May 27, 2015 at 9:13 AM, Prasenjit Ghosh <span dir="ltr"><<a href="mailto:prasenjit.jnc@gmail.com" target="_blank">prasenjit.jnc@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div><div><div>Dear all,<br><br></div>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.<br></div>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.<br>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).<br></div>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.<br> <br clear="all"><div><div><div><div>Similarly for the tethedra, for alpha=-0.2, the non-interacting response does not remain linear while for the interacting one it remains linear.<br><br></div><div>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? <br><br></div><div>Below is the input file I am using for the calculation:<br><br>for alpha in -0.20 -0.15 -0.10 -0.05 0.00 0.05 0.10 0.15 0.20 <br><br>do<br><br>mkdir /scratch/pghosh/octfe/alpha$alpha<br><br>cd /scratch/pghosh/octfe/alpha$alpha<br><br>ethr=`grep ethr /home/pghosh/Ca2Fe2O5/octfe/scf.out | tail -1 | awk '{print $3}'`<br><br>rm -rf Ca2Fe2O5-noU-vcrel-AFM.*<br><br>cp -r ../Ca2Fe2O5-noU-vcrel-AFM.* .<br><br>cat > scf-octFe.$<a href="http://alpha.in" target="_blank">alpha.in</a> << EOF<br> &control<br> calculation = 'scf',<br> prefix = 'Ca2Fe2O5-noU-vcrel-AFM',<br> outdir = '/scratch/pghosh/octfe/alpha$alpha'<br> pseudo_dir = '/home/pghosh/pseudo' <br> /<br> &system<br> ibrav = 0,<br> celldm(1)=10.25176385 <br> nat = 36, <br> ntyp = 5,<br> ecutwfc = 45<br> ecutrho = 320<br> nspin=2<br> starting_magnetization(2)=-1.0<br> starting_magnetization(3)=1.0<br> starting_magnetization(4)=-1.0<br> occupations='smearing'<br> degauss=0.001<br> smearing='gaussian'<br> lda_plus_u = .true.,<br> U_projection_type = 'atomic',<br> Hubbard_U(2) = 1.d-10<br> Hubbard_U(3) = 1.d-10<br> Hubbard_U(4) = 1.d-10<br> Hubbard_U(5) = 1.d-10<br> Hubbard_alpha(4) = $alpha<br> /<br> &electrons<br> mixing_beta = 0.3<br> conv_thr = 1.0d-8,<br> startingwfc = 'file',<br> startingpot = 'file',<br> diago_thr_init = $ethr<br> /<br><br>ATOMIC_SPECIES<br> Ca 87.62 Ca.pw91-nsp-van.UPF<br> Fe1 47.867 Fe.pw91-sp-van_ak.UPF<br> Fe2 47.867 Fe.pw91-sp-van_ak.UPF<br> Fe3 47.867 Fe.pw91-sp-van_ak.UPF<br> O 15.999 O.pw91-van_ak.UPF<br>ATOMIC_POSITIONS (crystal)<br>Ca 0.479439516 0.108738866 0.023376810<br>Ca 0.979439516 0.391261134 0.476623190<br>Ca 0.520560484 0.608738866 0.976623190<br>Ca 0.020560484 0.891261134 0.523376810<br>Ca 0.520560484 0.891261134 0.976623190<br>Ca 0.020560484 0.608738866 0.523376810<br>Ca 0.479439516 0.391261134 0.023376810<br>Ca 0.979439516 0.108738866 0.476623190<br>Fe3 0.000000000 0.000000000 -0.000000000<br>Fe1 0.500000000 0.500000000 0.500000000<br>Fe1 0.000000000 0.500000000 -0.000000000<br>Fe1 0.500000000 -0.000000000 0.500000000<br>Fe2 0.948517158 0.250000000 0.935170308<br>Fe2 0.448517158 0.250000000 0.564829692<br>Fe2 0.051482842 0.750000000 0.064829692<br>Fe2 0.551482842 0.750000000 0.435170308<br>O 0.262959232 0.985181682 0.237331409<br>O 0.762959232 0.514818318 0.262668591<br>O 0.737040768 0.485181682 0.762668591<br>O 0.237040768 0.014818318 0.737331409<br>O 0.737040768 0.014818318 0.762668591<br>O 0.237040768 0.485181682 0.737331409<br>O 0.262959232 0.514818318 0.237331409<br>O 0.762959232 0.985181682 0.262668591<br>O 0.027189198 0.140319152 0.069344138<br>O 0.527189198 0.359680848 0.430655862<br>O 0.972810802 0.640319152 0.930655862<br>O 0.472810802 0.859680848 0.569344138<br>O 0.972810802 0.859680848 0.930655862<br>O 0.472810802 0.640319152 0.569344138<br>O 0.027189198 0.359680848 0.069344138<br>O 0.527189198 0.140319152 0.430655862<br>O 0.586951586 0.250000000 0.888451999<br>O 0.086951586 0.250000000 0.611548001<br>O 0.413048414 0.750000000 0.111548001<br>O 0.913048414 0.750000000 0.388451999<br>K_POINTS (automatic)<br>9 3 9 1 1 1 <br>CELL_PARAMETERS (alat)<br> 0.991167212 0.000000000 0.000000000<br> 0.000000000 2.746908521 0.000000000<br> 0.000000000 0.000000000 1.023657125<br>EOF<br><br></div><div><br></div><div><br></div><div>With regards,<br><br></div><div>Prasenjit <br></div><span class="HOEnZb"><font color="#888888"><div>-- <br><div><div dir="ltr">PRASENJIT GHOSH,<br>IISER Pune,<br>Dr. Homi Bhabha Road, Pashan<br>Pune, Maharashtra 411008, India<br><br>Phone: <a href="tel:%2B91%20%2820%29%202590%208203" value="+912025908203" target="_blank">+91 (20) 2590 8203</a><br>Fax: <a href="tel:%2B91%20%2820%29%202589%209790" value="+912025899790" target="_blank">+91 (20) 2589 9790</a></div></div>
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