good! check and see if it is within the litt. values. cheers
Layla 2015-05-14 13:05 GMT+02:00 Khara, Galvin <galvin.khara...@ucl.ac.uk>: > Hey, > > > By using a value of 0.096, (Heyd recommends using a value smaller than > 0.15 to reproduce accurate band gaps in semi-conductors), my cutoff > energies oscillate as follows; (scf energy, ecut energy). > > > -14.56060124 > -14.56579225 -- 20 Ry > -14.56576890 > -14.56671699 -- 30 Ry > -14.56731443 > -14.56796231 -- 40 Ry > -14.56725086 > -14.56720876 -- 50 Ry > -14.56751976 > -14.56750677 -- 60 Ry > -14.56749110 > -14.56713377 -- 70 Ry > -14.56711227 > -14.56709019 -- 80 Ry > -14.56706889 > -14.56704906 -- 90 Ry > -14.56722966 > -14.56721482 -- 100 Ry > -14.56700415 > -14.56699186 -- 110 Ry > -14.56697995 > -14.56696887 -- 120 Ry > -14.56695845 > -14.56694874 -- 130 Ry > -14.56693973 > -14.56693137 -- 140 Ry > -14.56692360 > -14.56691649 -- 150 Ry > -14.56690962 > -14.56690322 -- 160 Ry > -14.56698048 > -14.56697473 -- 170 Ry > -14.56696928 > -14.56696413 -- 180 Ry > -14.56693442 > -14.56692978 -- 190 Ry > -14.56692543 > > > > So the oscillation isn't massive, but I am only using a 2-atom cell. I > am basically interested in calculating the energy of my system at elevated > electronic temperatures (using femi-dirac smearing), I'm going to go ahead > and calculate my band-gap and lattice parameters using this oscillating > ecut, and see how close they are to literature. Do you think this is ill > advised? > > > Thanks, > > > Galvin > ------------------------------ > *From:* Layla Martin-Samos <lmartinsa...@gmail.com> > *Sent:* 14 May 2015 09:57 > > *To:* PWSCF Forum > *Subject:* Re: [Pw_forum] Silicon HSE Problem > > Hi, I think that the safest way is to increase the dimension of your > simulation cell (by replicating the unit cell along the three axes) and use > the screening param that gives you the correct gap. To have uncontrolled > noise may be a source of "random numbers". However, each researcher is > responsible for the numbers he publish. The impact of noise depends also on > the precision and accuracy that you will need or that you expect to need > for further post-processing/analysis/multiscale ... . Personally, I try to > have initial steps as good as I can, because for my research a > not-that-good initial step has a big and negative impact in the next steps. > > cheers > > Layla > > 2015-05-12 15:19 GMT+02:00 Khara, Galvin <galvin.khara...@ucl.ac.uk>: > >> Hey, >> >> >> 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)? >> >> >> Thanks, >> >> >> Galvin >> ------------------------------ >> *From:* Layla Martin-Samos <lmartinsa...@gmail.com> >> *Sent:* 10 April 2015 14:39 >> *To:* PWSCF Forum >> *Subject:* Re: [Pw_forum] Silicon HSE Problem >> >> Hi Galvin, maybe the screening_parameter ( HSE has two parameters >> exx_fraction and screening_parameter) is not big/small (I never >> remember if it is dividing or multiplying) enough for your small cell. >> Maybe you could try to check the behavior of the total Energy >> convergence with respect to variations of this parameter. (in >> principle this parameter control the decay of the short range part of >> the coulomb potential in your cell. If the short range part is not >> small enough at the borders you may find funny results). >> >> cheers >> >> Layla >> >> 2015-04-10 15:20 UTC+02:00, Khara, Galvin <galvin.khara...@ucl.ac.uk>: >> > ?Hey, >> > >> > >> > >> > I've been trying to use the HSE hybrid in QE to do some simulations on >> Si. >> > I'm finding that increasing my ecutwfc is causing the total energy to >> > oscillate quite significantly. This seems to indicate a big problem as >> this >> > should always converge as it is variational.? When I use the plain PBE >> > (Si.pbe-hgh.upf) pseudopotential without invoking any hybrid functional >> the >> > energy converges as expected. >> > >> > >> > It only starts to oscillate when I add the input_dft='hse' directive, >> I >> > have not added anything non-standard to my input as far as I know (the >> > default values for nqx, x_gamma_extrapolation, and exxdiv_treatment? are >> > used). My input file is as follows, >> > >> > >> > " >> > >> > &control >> > prefix='silicon', >> > pseudo_dir = '~/pseudo' >> > outdir='~/tmp' >> > tprnfor = .true. >> > tstress = .true. >> > / >> > &system >> > ibrav = 1, celldm(1) =10.18, nat= 8, ntyp= 1, >> > ecutwfc = $alat, >> > occupations='smearing', >> > degauss=0.002, smearing='gaussian', >> > input_dft='hse' >> > / >> > &electrons >> > scf_must_converge= .true. >> > conv_thr = 1.0e-12 >> > mixing_beta = 0.7 >> > / >> > ATOMIC_SPECIES >> > Si 28.0855 Si.pbe-hgh.upf >> > >> > ATOMIC_POSITIONS crystal >> > Si 0.0 0.0 0.0 >> > Si 0.5 0.5 0.0 >> > Si 0.5 0.0 0.5 >> > Si 0.0 0.5 0.5 >> > Si 0.25 0.25 0.25 >> > Si 0.75 0.75 0.25 >> > Si 0.75 0.25 0.75 >> > Si 0.25 0.75 0.75 >> > >> > K_POINTS gamma >> > >> > >> > " >> > >> > >> > Also, I ultimately want to use the HSE hybrid to study Si at elevated >> > electronic temperatures (up to 25,000 K) via fermi-dirac broadening, is >> this >> > unrealistic / unwise with this choice of hybrid? Any help is greatly >> > appreciated. >> > >> > >> > >> > Thanks, >> > >> > >> > Galvin K, >> > Ph.D Researcher, >> > University College London >> > >> >> >> _______________________________________________ >> Pw_forum mailing list >> Pw_forum@pwscf.org >> http://pwscf.org/mailman/listinfo/pw_forum >> > > > _______________________________________________ > Pw_forum mailing list > Pw_forum@pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum >
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