Non self-consistent calculations: Band structures and Density Of States

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Non self-consistent calculations: Intro

Silicon band structure. Originals from [https://www.tf.uni-kiel.de/matwis/amat/td_kin_ii/index.html Thermodynamics and Kinetics II, Dr. J. Carstensen, Univ. Kiel]

Once the charge density has been obtained in a scf run, more calculations can be performed at fixed density (non-scf). Among these:

• calculations of Kohn-Sham energies and orbitals on any given set of k-points (i.e. without specific aim of represent a reasonable sampling of the BZ);
• calculations as above, also increasing the number of computed (= diagonalized) bands (incl the calculation of empty Kohn-Sham states);
• Importantly, nscf calculations are typically done to plot KS bands or compute the DOS,
• but also as a preliminary step to other calculations (e.g. uniform k-point samplings and large amounts of empty states are using in GW and other many-body perturbation theory algorithms implemented with sum-over-states techniques)

In the Quantum ESPRESSO input file one has to set:

   calculation="nscf"     # kpts sampling BZ

or

   calculation="bands"   # kpts along lines

K-points (and number of bands if relevant) need to be specified.