[QE-users] Fwd: under estimate the bandgap in Quantum espresso
PRASAD SANKALPA WANNINAYAKA
2019s17502 at stu.cmb.ac.lk
Sat Feb 17 02:26:41 CET 2024
Dear Omar Ashour,
thanks for your valuable suggestions. yes, I'm using U values obtained by
linear response calculation. And I have performed relaxation calculations
for the structure. I found that there is an issue can anyone know about
this, can you please explain this? "When performing DFT+U calculation, the
ground state might get stuck in a *local minimum*, in such cases we need to
provide starting_ns_eigenvalue to help calculation reach desired/actual
ground state."
best regards,
Prasad Sankalpa
On Sat, Feb 17, 2024 at 12:10 AM Omar Ashour via users <
users at lists.quantum-espresso.org> wrote:
> I have not checked your input files but here are a couple of thoughts
> based on your opening paragraph.
>
> Hybrid functionals usually lead to larger band gaps compared to semi-local
> functionals like PBE. You should compare to a reference using PBE+U. Use
> ortho-atomic projectors for DFT+U. How did you get your U value? You can
> try computing it with linear response using the hp.x code.
>
> Further, the materials project structures are done in a high throughput
> manner and I always recommend you relax them again properly for your own
> projects. They are also computed in VASP-- relaxation results are, strictly
> speaking, not transferable between codes/pseudo potentials. You should
> check the pressure/stress and forces in your cell when using a structure
> you didn't relax yourself and judge whether they're reasonable.
>
> Best,
>
> Omar A. Ashour
> UC Berkeley
>
> On Feb 16, 2024, at 4:52 AM, PRASAD SANKALPA WANNINAYAKA <
> 2019s17502 at stu.cmb.ac.lk> wrote:
>
>
> Dear Dr.Giovanni Cantele,
> Thanks for your reply, I'm using the DFT + U method for calculations. I'm
> following the materials project site as the base reference for the
> structure. that bandgap value was obtained from the references that follow
> the hybrid density functional method. I have attached the SCF and band
> calculation inputs file below. Can please check these input files.
>
> Thank you,
>
> &CONTROL
> calculation = 'scf',
> restart_mode = 'from_scratch',
> prefix = 'bands',
> outdir = './tmp/'
> pseudo_dir = './psuedo_sr'
> verbosity = 'high'
> /
>
> &SYSTEM
> ibrav = 4,
> a = 5.14011, c = 13.82966,
> cosBC = 0,
> cosAC = 0,
> cosAB = -0.5,
> nat = 30, ntyp = 4,
> ecutwfc = 50,
> ecutrho = 400.0,
> nbnd = 280
> occupations = 'smearing', degauss = 0.001, smearing = 'gaussian',
> nspin=2,
> starting_magnetization(1) = 4
> starting_magnetization(2) = -4
> starting_magnetization(3) = 0
> starting_magnetization(4) = 0
> /
>
> &electrons
> conv_thr = 1.0e-7
> electron_maxstep = 500
> mixing_beta = 0.3d0
> /
>
> ATOMIC_SPECIES
> Fe1 55.845 Fe.pbe-spn-kjpaw_psl.1.0.0.UPF
> Fe2 55.845 Fe.pbe-spn-kjpaw_psl.1.0.0.UPF
> Ti 47.867 Ti.pbe-spn-kjpaw_psl.1.0.0.UPF
> O 15.999 O.pbe-n-kjpaw_psl.1.0.0.UPF
>
> ATOMIC_POSITIONS (crystal)
> Ti 0.333333671 0.666666687 0.019728789
> Ti 0.333333671 0.666666687 0.313609332
> Ti 0.000000000 0.000000000 0.353068292
> Ti 0.000000000 0.000000000 0.646931648
> Ti 0.666667104 0.333333343 0.686390758
> Ti 0.666667104 0.333333343 0.980271161
> Fe1 0.000000000 0.000000000 0.141661420
> Fe2 0.666667104 0.333333343 0.191701844
> Fe2 0.666667104 0.333333343 0.474968076
> Fe1 0.333333671 0.666666687 0.525031984
> Fe1 0.333333671 0.666666687 0.808297873
> Fe2 0.000000000 0.000000000 0.858338833
> O 0.679246187 0.972118676 0.254297256
> O 0.027881473 0.707126856 0.254297256
> O 0.292873383 0.320754439 0.254297256
> O 0.987438619 0.361118644 0.079032004
> O 0.373680741 0.012561911 0.079032004
> O 0.638881803 0.626319408 0.079032004
> O 0.345913947 0.305455208 0.587620795
> O 0.694545090 0.040458456 0.587620795
> O 0.959542215 0.654086351 0.587620795
> O 0.654086947 0.694544613 0.412379205
> O 0.040458292 0.345913559 0.412379205
> O 0.305455744 0.959541857 0.412379205
> O 0.012562054 0.638881326 0.920967937
> O 0.361118942 0.373680562 0.920967937
> O 0.626320004 0.987438083 0.920967937
> O 0.320754468 0.027881414 0.745702744
> O 0.707127631 0.679245710 0.745702744
> O 0.972119093 0.292872876 0.745702744
>
> K_POINTS (automatic)
> 7 7 3 0 0 0
> HUBBARD (atomic)
> U Fe1-3d 5.3
> U Fe2-3d 5.3
>
> best regards
> Prasad Sankalpa
>
>
> On Fri, Feb 16, 2024 at 4:06 PM Giovanni Cantele <
> giovanni.cantele at spin.cnr.it> wrote:
>
>> Dear
>> Prasad, there are not sufficient data to understand what's happening.
>>
>> 1) DFT systematically underestimates band gaps, to what extent depends on
>> the material. If this is the case there is nothing to do unless moving to
>> other approximations that at least partially solve this problem
>> (DFT+U,hybrid functionals,GW,....)
>> 2) do the references you mention concern theoretical estimations within
>> DFT or experimental data? While when comparing with experiments you
>> might experient the limit of the previous point, whereas if you find
>> other calculations, within the same level of approximation, you should find
>> at least
>> similar (if not equal) results
>> 3) in the case you have reference calculations to compare with and there
>> is no agreement, check your input geometry and unit cell (to understand if
>> they
>> are wrong) as well as the convergence parameters (Brillouin zone
>> sampling, wave function cutoff, charge density cutoff if it applies, ....)
>>
>> Giovanni
>>
>> --
>>
>> Giovanni Cantele, PhD
>> CNR-SPIN
>> c/o Dipartimento di Fisica
>> Universita' di Napoli "Federico II"
>> Complesso Universitario M. S. Angelo - Ed. 6
>> Via Cintia, I-80126, Napoli, Italy
>> e-mail: giovanni.cantele at spin.cnr.it <giovanni.cantele at spin.cnr.it>
>> Phone: +39 081 676910
>> Skype contact: giocan74
>>
>> ResearcherID: http://www.researcherid.com/rid/A-1951-2009
>> Web page: https://sites.google.com/view/giovanni-cantele/home
>>
>>
>> Il giorno ven 16 feb 2024 alle ore 10:40 PRASAD SANKALPA WANNINAYAKA <
>> 2019s17502 at stu.cmb.ac.lk> ha scritto:
>>
>>> Dear QE users,
>>> I am studying the electronic properties of FeTiO3 using QE when
>>> calculating the band structure using 'bands.x' calculation. I obtained the
>>> bandgap as 0.01eV but according to references that value is 2.54 eV. i need
>>> to know why this is happening.
>>>
>>> Thank you
>>> Best regards
>>> Prasad Sankalpa
>>> Physics Undergraduate
>>>
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> <FeTiO3_bands.in>
> <FeTiO3_scf.in>
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> The Quantum ESPRESSO community stands by the Ukrainian
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