[QE-users] Fwd: under estimate the bandgap in Quantum espresso
PRASAD SANKALPA WANNINAYAKA
2019s17502 at stu.cmb.ac.lk
Fri Feb 16 13:51:27 CET 2024
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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