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 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
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
Il giorno ven 16 feb 2024 alle ore 10:40 PRASAD SANKALPA WANNINAYAKA < [email protected]> 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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