Variation in Anion-Anion Core-Shell Charges Across Different Cases

GULP
1

Why do anion-anion core-shell charge distributions vary across different cases?

What factors influence these charge variations in a core-shell model?

Are there specific guidelines to ensure consistency in charge assignment for anions in different simulations?

I have attached snippet of my input file.

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I have also attached snippet where a varied anion-anion core-shell charge has been considered.
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Any guidance would be greatly appreciated.

Best regards,
Aravind

2

A good start would be to read the Phil. Mag. B reference for fitting and potentials in GULP where the shell model is discussed. There are also references to the literature on earlier shell models & how they were fitted.