I am studying a material that is an insulator in its bulk form. When I convert
the system into a slab geometry and run SCF/NSCF calculations in Quantum
ESPRESSO, I see unexpected behavior in the electronic structure (large shifts
in HOMO/LUMO levels ).
With Occupations =Fixed
Highest occupied and Lowest unoccupied level (ev): -0.1520 1.5853 from
scf.out.
Highest occupied, lowest unoccupied level (ev): 5.8411 11.1794 from
nscf.out.
With Occupations="smearing"
degauss=0.02
smearing="gaussian"
I am getting the Fermi energy is 0.7314 ev----nscf
(compare with: 0.7311 eV, computed in scf)
Since the material is insulating in bulk but behaves differently when modeled
as a slab, should I be using a different method or setting for slab
calculations? How do we determine occupations parameter in such cases?
Chandrika Yadav K
Research Scholar
NanoElectronics Laboratory
Amrita Viswa Vidyapeetham
Bangalore
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