In my knowledge HSE06 is with 0.2 screening parameter and if you convert 0.106 to A^-1 then its 0.106/0.529=0.2. There is HSE03 also, I don't remember the screening parameter there.
On Fri, May 22, 2015 at 5:04 PM, Khara, Galvin <[email protected]> wrote: > Hey, > > > Are you sure about this conversion factor? Because the default value > that espresso will take for the screening parameter is 0.106, and Heyd > recommends using a value less than 0.15 to get a correct band gap (and most > literature taking a value between 0.1 and 0.15). So this conversion would > yield quite different results no? > > > > Thanks, > > > Galvin > ------------------------------ > *From:* DHIRENDRA VAIDYA <[email protected]> > *Sent:* 22 May 2015 08:45 > > *To:* PWSCF Forum > *Subject:* Re: [Pw_forum] Silicon HSE Problem > > Hi Galvin, > > Checkout the units of screening parameter. I think HSE06 screening > parameter is 0.2 Angstroms^-1. And I think PWSCF accepts screening > parameter in Bohr^-1. So 0.0916 would correspond to ~0.173A^-1. > > On Fri, May 22, 2015 at 11:41 AM, Khara, Galvin <[email protected] > > wrote: > >> Hey, >> >> >> Thanks for your reply. Using an ecut of 60 Ry, a 8x8x8 kpoint grid (and >> also an 8x8x8 nqx grid), and a screening parameter of 0.0916, I got a value >> of 1.19 eV using the method you outlined. Is that a bit too good to be >> true? Heyd's original thesis quotes a value of 1.31 eV for silicon, but >> that was using a screening parameter of 0.15, which may account for the >> difference. Have you attempted to obtain bandstructure graph by using a >> defined uniform k-point list for the 2nd scf calculation? I'd like to know >> how to do this just with the eigenvalues (sorry for the novice questions), >> and thanks again for your reply. >> >> >> >> Galvin, >> University College London >> ------------------------------ >> *From:* DHIRENDRA VAIDYA <[email protected]> >> *Sent:* 20 May 2015 20:40 >> >> *To:* PWSCF Forum >> *Subject:* Re: [Pw_forum] Silicon HSE Problem >> >> Hi Galvin, >> >> I am also looking at HSE bandstructure calculaitons, mainly for Group IV >> elements from semiconductore point of view. I get from PWSCF forum that its >> difficult to obtain the bandstructure using HSE, but bandgap might be easy >> to obtain. Try this, >> In scf calculations add, nbnd (=8 if using 2 atom FCC lattice for >> Silicon). Remove 'occumpations='smearing''. And then do scf calculations >> first without HSE and then with HSE with 'restart_mode='restart''. In >> output file you will find something like this, >> highest occupied, lowest unoccupied level (ev): #some_value1 >> #some_value2 >> >> the difference is the bandgap = #some_value2-#some_value1 >> >> On Wed, May 20, 2015 at 6:54 PM, Khara, Galvin <[email protected] >> > wrote: >> >>> Hey, >>> >>> >>> I'm getting a value of 5.445 Angstroms for my lattice paramter, which >>> is pretty close to the value quoted by Heyd (5.45), and that using a >>> different screening parameter (which he says does alter the physical >>> properties anyway). The next thing I want to do is calculate the band >>> gap, searching through the archives actually gives loads of topics on this >>> very problem. However, I'm really new to DFT, is there any chance you could >>> provide a method to do this, so far I've understood; >>> >>> >>> (i) - Do a regular scf calculation using an automatic fine k-point >>> mesh (I'm running an 8x8x8 simulation now) >>> >>> >>> (ii) - Run another scf calculation with a defined k-point list (does >>> this k-point list depend at all on my choice of NxNxN in (i)). Can I choose >>> any the standard 28 k-points quoted in example01? >>> >>> >>> (iii) - How do I actually calculate my band gap from the eigenvalues >>> outputted from this 2nd scf? >>> >>> >>> Sorry about my ignorance on this. To compare it with the literature >>> band gap, would it also be possible to just use the dos post processing >>> tool? I will be needing the dos at some point in the future anyway. Is this >>> used in the same way as it is for non-hybrid functionals? >>> >>> >>> Thank you so much for taking the time to read this. It's really >>> appreciated. >>> >>> >>> Galvin, >>> UCL. >>> ------------------------------ >>> *From:* Layla Martin-Samos <[email protected]> >>> *Sent:* 14 May 2015 13:10 >>> >>> *To:* PWSCF Forum >>> *Subject:* Re: [Pw_forum] Silicon HSE Problem >>> >>> good! check and see if it is within the litt. values. >>> >>> cheers >>> >>> Layla >>> >>> 2015-05-14 13:05 GMT+02:00 Khara, Galvin <[email protected]>: >>> >>>> 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 <[email protected]> >>>> *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 <[email protected]>: >>>> >>>>> 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 <[email protected]> >>>>> *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 <[email protected]>: >>>>> > ?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 >>>>> [email protected] >>>>> http://pwscf.org/mailman/listinfo/pw_forum >>>>> >>>> >>>> >>>> _______________________________________________ >>>> Pw_forum mailing list >>>> [email protected] >>>> http://pwscf.org/mailman/listinfo/pw_forum >>>> >>> >>> >>> _______________________________________________ >>> Pw_forum mailing list >>> [email protected] >>> http://pwscf.org/mailman/listinfo/pw_forum >>> >> >> >> >> -- >> -- >> Dhirendra >> >> _______________________________________________ >> Pw_forum mailing list >> [email protected] >> http://pwscf.org/mailman/listinfo/pw_forum >> > > > > -- > -- > Dhirendra > > _______________________________________________ > Pw_forum mailing list > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum > -- -- Dhirendra
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