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PAOs for anions
Date: 2016/10/01 03:40
Name: Daniil

Dear all,
as I see from databases, cutoff radii of PAOs are in general proportional to atomic or covalent radii of corresponding elements. For example, PAOs for calcium are almost twice as large than ones for oxygen.
But for ionic crystals, ionic radii are more significant for estimating cutoff spheres, and it is especially important in case of anions, for which ionic radii are greater than covalent.
So, I hope there is either an explanation, why should small cutoff radii work for anions, or a possibility to obtain larger PAOS.

Thanks, Daniil.
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Re: PAOs for anions ( No.1 )
Date: 2016/10/16 22:09
Name: T. Ozaki


In case of neutral atoms, the proper cutoff radius is (approximately) inversely proportional
to the number of coordination atoms, which is a consequence of the virial theorem.
The isolated atom has a longer tail, while the PAOs shrink in the densely packed system
such as FCC. In case of anions, there are two factors governing the tail: one is the
coordination number and the other the anionicity. When we consider anions in bulks,
PAO tryies to shrink due to the former and to delocalize due to the latter.
Thus, we expect that the the proper cutoff may be similar to that of isolated atom, while
the expectation may not be true in some cases such as anions having low-coordination.



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