[Pw_forum] Silicon HSE Problem
DHIRENDRA VAIDYA
dhirendra22121987 at gmail.com
Sat May 23 02:39:48 CEST 2015
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 <galvin.khara.12 at ucl.ac.uk>
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 <dhirendra22121987 at gmail.com>
> *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 <galvin.khara.12 at ucl.ac.uk
> > 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 <dhirendra22121987 at gmail.com>
>> *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 <galvin.khara.12 at ucl.ac.uk
>> > 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 <lmartinsamos at gmail.com>
>>> *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 <galvin.khara.12 at 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 <lmartinsamos at 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.12 at 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 <lmartinsamos at 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.12 at 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 at pwscf.org
>>>>> http://pwscf.org/mailman/listinfo/pw_forum
>>>>>
>>>>
>>>>
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>>
>>
>> --
>> --
>> Dhirendra
>>
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>
>
>
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> Dhirendra
>
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Dhirendra
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