- Why do we specifically need an SCF-generated charge density for calculating the density of states (DOS) and band structure?
- How does using ISMEAR=0 or ISMEAR=-5 affect the calculation of DOS?
- Is it possible to initiate the calculation with ICHARGE=2 for DOS calculations?
Dear Trivanni Yadav,
You should specify that your questions are about VASP so people can help you more directly. I can indeed only answer your first question, but I believe the other two should be in VASP manual…
In general, we do not need to specifically start from a SCF charge density. You can start from whatever proper density (that is, a definite positive function integrable to the number of electrons in your system). The way you obtain that charge density somewhat defines the level of accuracy of your calculation. For example, if you had access to Monte Carlo-calculated densities, those would provide an excellent starting point for further calculations. You could construct a density starting from a linear combination of the occupied atomic orbitals. Clearly this density would be a poor starting point as we know it neglects important correlation effects.
In the case of DFT, to obtain the charge density you have to solve the non-linear Kohn-Sham equations for your system. An efficient, robust, and general method to solve non-linear equations relies on self-consistent loops. The same method, for instance, can be used to solve the Hartree-Fock equations. So there is nothing inherently magic into the “SCF-generated charged density” if not a general method of numerical solution.
I hope this helps clarifying your doubts,
Roberto
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