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<p>Hey,<br>
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<p>Sorry to bring up an old topic, but from reading the HSE paper, I need the screening parameter to be between 0.1 and 0.2 for a correct band gap calculation in silicon. Is it a bad idea to use a value for ecut that is oscillating (but not by a huge amount)?<br>
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<p>Thanks,<br>
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<div>Galvin<br>
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<div id="x_divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> Layla Martin-Samos <lmartinsamos@gmail.com><br>
<b>Sent:</b> 10 April 2015 14:39<br>
<b>To:</b> PWSCF Forum<br>
<b>Subject:</b> Re: [Pw_forum] Silicon HSE Problem</font>
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<div class="PlainText">Hi Galvin, maybe the screening_parameter ( HSE has two parameters<br>
exx_fraction and screening_parameter) is not big/small (I never<br>
remember if it is dividing or multiplying) enough for your small cell.<br>
Maybe you could try to check the behavior of the total Energy<br>
convergence with respect to variations of this parameter. (in<br>
principle this parameter control the decay of the short range part of<br>
the coulomb potential in your cell. If the short range part is not<br>
small enough at the borders you may find funny results).<br>
<br>
cheers<br>
<br>
Layla<br>
<br>
2015-04-10 15:20 UTC+02:00, Khara, Galvin <galvin.khara.12@ucl.ac.uk>:<br>
> ?Hey,<br>
><br>
><br>
><br>
> I've been trying to use the HSE hybrid in QE to do some simulations on Si.<br>
> I'm finding that increasing my ecutwfc is causing the total energy to<br>
> oscillate quite significantly. This seems to indicate a big problem as this<br>
> should always converge as it is variational.? When I use the plain PBE<br>
> (Si.pbe-hgh.upf) pseudopotential without invoking any hybrid functional the<br>
> energy converges as expected.<br>
><br>
><br>
> It only starts to oscillate when I add the input_dft='hse' directive, I<br>
> have not added anything non-standard to my input as far as I know (the<br>
> default values for nqx, x_gamma_extrapolation, and exxdiv_treatment? are<br>
> used). My input file is as follows,<br>
><br>
><br>
> "<br>
><br>
> &control<br>
> prefix='silicon',<br>
> pseudo_dir = '~/pseudo'<br>
> outdir='~/tmp'<br>
> tprnfor = .true.<br>
> tstress = .true.<br>
> /<br>
> &system<br>
> ibrav = 1, celldm(1) =10.18, nat= 8, ntyp= 1,<br>
> ecutwfc = $alat,<br>
> occupations='smearing',<br>
> degauss=0.002, smearing='gaussian',<br>
> input_dft='hse'<br>
> /<br>
> &electrons<br>
> scf_must_converge= .true.<br>
> conv_thr = 1.0e-12<br>
> mixing_beta = 0.7<br>
> /<br>
> ATOMIC_SPECIES<br>
> Si 28.0855 Si.pbe-hgh.upf<br>
><br>
> ATOMIC_POSITIONS crystal<br>
> Si 0.0 0.0 0.0<br>
> Si 0.5 0.5 0.0<br>
> Si 0.5 0.0 0.5<br>
> Si 0.0 0.5 0.5<br>
> Si 0.25 0.25 0.25<br>
> Si 0.75 0.75 0.25<br>
> Si 0.75 0.25 0.75<br>
> Si 0.25 0.75 0.75<br>
><br>
> K_POINTS gamma<br>
><br>
><br>
> "<br>
><br>
><br>
> Also, I ultimately want to use the HSE hybrid to study Si at elevated<br>
> electronic temperatures (up to 25,000 K) via fermi-dirac broadening, is this<br>
> unrealistic / unwise with this choice of hybrid? Any help is greatly<br>
> appreciated.<br>
><br>
><br>
><br>
> Thanks,<br>
><br>
><br>
> Galvin K,<br>
> Ph.D Researcher,<br>
> University College London<br>
><br>
<br>
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