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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 ).</div>
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With Occupations =Fixed </div>
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Highest occupied and Lowest unoccupied level (ev): -0.1520 1.5853 from scf.out. </div>
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Highest occupied, lowest unoccupied level (ev): 5.8411 11.1794 from nscf.out. </div>
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With Occupations="smearing" </p>
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degauss=0.02</p>
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smearing="gaussian"</p>
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I am getting the Fermi energy is 0.7314 ev----nscf</p>
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(compare with: 0.7311 eV, computed in scf)</div>
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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?</div>
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Chandrika Yadav K</div>
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Research Scholar</div>
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NanoElectronics Laboratory </div>
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Amrita Viswa Vidyapeetham </div>
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Bangalore </div>
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