Thank you Prof. Giovanni Cantele,for your insightful response.
Here is a brief update on the tests I performed.
Tested denser k-meshes for the NSCF calculation as suggested, 48x48x1 and
72x72x1, and also performed a vacuum convergence test with several vacuum
thicknesses, but in the strained (compressive strain of 3%) unit cell (Figure
2), additional states at the edge of the conduction band are still visible, and
also the total DOS is not accounted by either the B or N projected DOS
individually or collectively.
Further, I have started the |psi|^2 visualization using pp.x as advised and
will update this thread with the results once the analysis is finished.
Below I have shared nscf input file for reference.
# denser k mesh
&CONTROL
calculation = 'nscf'
prefix = ' --------'
outdir = '--------- '
pseudo_dir = '-------- '
/
&SYSTEM
ibrav = 4 ! Hexagonal lattice
celldm(1) = 4.592 ! a in Bohr ::2.43Å
celldm(3) = 8.23 !20 A vaccum
nat = 2
ntyp = 2
ecutwfc = 60
ecutrho = 480
nbnd =8
occupations = 'smearing'
smearing = 'gaussian'
degauss = 0.01
/
&ELECTRONS
conv_thr = 1.0d-8
mixing_beta = 0.4
/
ATOMIC_SPECIES
B 10.811 B.pbe-n-rrkjus_psl.1.0.0.UPF
N 14.007 N.pbe-n-rrkjus_psl.1.0.0.UPF
ATOMIC_POSITIONS (crystal)
B 0.6667000000 0.3333000000 0.0000000000
N 0.3333000000 0.6667000000 0.0000000000
K_POINTS {automatic}
48 48 1 0 0 0
Chandrika Yadav K
Research Scholar
NanoElectronics Laboratory
Amrita Viswa Vidyapeetham
Bangalore
________________________________
From: Giovanni Cantele <[email protected]>
Sent: Thursday, March 26, 2026 3:31 PM
To: Ms. Chandrika K. <[email protected]>; Quantum
ESPRESSO users Forum <[email protected]>
Subject: Re: [QE-users] Extra states in conduction band and PDOS/Total DOS
mismatch in strained hBN unit cell
Hi,
generally speaking, it is expected that, as one moves to higher energies (in
the unoccupied manifold), the sum of the projected DOS over all atoms/species
becomes smaller than the total DOS.
This is because projwfc.x projects Kohn–Sham states onto atomic wavefunctions
defined in the pseudopotential files. These atomic functions are constructed to
describe well the valence states and,
to some extent, low-lying unoccupied states. However, higher-energy states may
contain components that are not well represented within this atomic-like basis,
and therefore are only partially captured
by the projections. You can directly observe this behavior in the projwfc.x
output: the quantity reported after each eigenvalue (the sum of projections,
i.e. |psi|^2 onto the atomic basis) is typically very close to
1 for occupied states, while it starts to decrease for unoccupied states and
continues to do so with increasing energy.
That said, it is important to understand whether your specific observation has
a physical origin or is instead a numerical artifact. A few points you may want
to check:
- while a 36×36×1 grid for NSCF should already give a reasonable DOS, I would
still test denser meshes. The presence of many peaks in your DOS
could indicate insufficient Brillouin zone sampling rather than a physical
effect;
- identify the k-points and energies corresponding to the states at the
conduction band edge in the strained system, and visualize the corresponding
|psi|^2 (e.g. with pp.x).
If these states are more delocalized in the interstitial or vacuum region,
rather than localized on B/N atoms or bonds, then it is expected that atomic
projections do not fully capture them;
- is this bulk or monolayer hBN? In the monolayer case, vacuum regions can play
an important role, and low-lying conduction states may have significant weight
outside the atomic regions.
Did you check, if it applies, convergence with respect to the vacuum?
- make sure the strain has been applied consistently and that atomic positions
have been properly relaxed. Geometrical inconsistencies can lead to spurious
states near the band edges;
- sharing input files and band structure plots would help to better assess
whether the observed features are physical.
Giovanni
--
Prof. Giovanni Cantele
Dipartimento di Fisica "Ettore Pancini"
Universita' degli Studi di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
e-mail: [email protected]<mailto:[email protected]>
Phone: +39 081 676910
Web page: https://sites.google.com/view/giovanni-cantele/home
Il giorno gio 26 mar 2026 alle ore 09:35 Ms. Chandrika K. via users
<[email protected]<mailto:[email protected]>> ha
scritto:
Hello everyone,
I am performing DFT calculations on a pristine and uniaxially strained
hexagonal boron nitride (hBN) unit cell using Quantum ESPRESSO with the
following computational parameters:
* Pseudopotentials: B.pbe-n-rrkjus_psl.1.0.0.UPF and
N.pbe-n-rrkjus_psl.1.0.0.UPF (USPP, PBE, scalar relativistic)
* ecutwfc: 60 Ry | ecutrho: 480 Ry
*
K-mesh: 12×12×1 (SCF), 36×36×1 (NSCF)
* Broadening: ngauss = 0, degauss = 0.004 Ry, DeltaE = 0.004 eV
*
DOS tool: projwfc.x only (both total DOS and PDOS from same run)
*
Basis: Only s and p orbitals present for both B and N
*
In the pristine unit cell DOS (Figure 1), the total DOS and the sum of B and N
projected DOS match upto certain point in the conduction band.
*
However, in the strained unit cell (Figure 2), additional states at the edge of
conduction band are visible and also the total DOS is not accounted by either
the B or N projected DOS individually or collectively.
Any insights on the origin of the extra conduction band states and the enhanced
PDOS mismatch in the strained system would be greatly appreciated.
Chandrika Yadav K
Research Scholar
NanoElectronics Laboratory
Amrita Viswa Vidyapeetham
Bangalore
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_______________________________________________________________________________
The Quantum ESPRESSO Foundation stands in solidarity with all civilians
worldwide who are victims of terrorism, military aggression, and indiscriminate
warfare.
--------------------------------------------------------------------------------
Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
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