We are all aware of the fact that negative charge densities in the atomic cores are an artefact of Density Functional theory Calculations using Projector Augmented Wave (PAW) method. But what is the justification for these negative charges? They certainly did not appear out of nowhere. I request an explanation and a convincing proof if available.

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    $\begingroup$ I'm not sure what you mean by "proof", they arise directly from the augmentation charges in the PAW (or ultrasoft) method. The way these methods work is they rearrange the charge density inside the core region, but this charge rearrangement is computed for a reference system which is usually an isolated neutral atom. When used in a material, it's entirely possible that they "remove" more charge density than there actually is, which leads to negative charge densities there. This can also arise from aliasing, if you have too low a plane-wave cut-off energy. Is that what you meant? $\endgroup$ Oct 9, 2021 at 22:36
  • $\begingroup$ Pranoy, this question has remained in the unanswered queue for over 4 months now, so I wonder if Phil Hasnip's comment was helpful and/or whether or not you can answer his questions to make it easier to get an answer? $\endgroup$ Dec 31, 2021 at 1:02
  • $\begingroup$ This question appears to be abandoned. It can be reopened if the OP addresses questions/suggestions in the comments or anyone else wants to give an answer. $\endgroup$
    – Tyberius
    Jan 14, 2022 at 1:36