[QE-users] Extra states in conduction band and PDOS/Total DOS mismatch in strained hBN unit cell

[Giovanni Cantele]

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: giovanni.cantele at unina.it
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 <
users at lists.quantum-espresso.org> 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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