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By default LDIAG = .TRUE. However, setting LDIAG = .FALSE. selects Loewdin perturbation theory for the subspace rotation matrix which is much faster but generally significantly less stable for metallic and small gap systems. [1] Given the previous statement, what constitutes a small band gap when using VASP? Are band gaps of 0.25, 0.5, or 1 eV all considered small or are neither considered small? Thanks in advance for your consultation.

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[1] http://cms.mpi.univie.ac.at/vasp/vasp/I ... G_tag.html


<span class='smallblacktext'>[ Edited ]</span>

This is not strictly defined. "Small gap" behaviour depends also on the shape of the cell. In general "small gap" is smaller than approximately 0.5 eV. Cells extended in one dimension can exhibit "small gap" behaviour up to 1 eV.

Thank you!