[Pw_forum] questions on lattice dynamical principle

[degironc]

good questions... why don't you ask the authors ?
stefano

luch001 wrote:

> Dear all:
>
> I have read the paper titled ¡°Theory of systematic absence of
> NaCl-type (¦Â-Sn-type) high pressure phases in covalent (ionic)
> semiconductors¡± (Phys Rev Lett. *82*, 767, 1999). The phonon behaviors
> are dominated by the competition between the attractive electrostatic
> Madelung energy ¨CZ^2 /R (where Z is the excess charge within the
> atomic sphere) and the repulsive short-range energy.I can not
> understand well the formula of the force constant given in the last
> part of page 769. I thought to present the formula here.
> Unfortunately, I can not add it in my email text. I am very sorry for
> that.
>
> How does it come from? Does it apply to all the systems or just apply
> to some specific system? The values of A and ¦Ë are determined by what
> factors?
>
> The authors claimed that the transverse acoustic mode at X point
> lowers the repulsive energy and raises the Madelung energy, but why?
>
> I have pondered hardly and consulted with others. But I have reached
> no conclusion.
>
> Any reply will be appreciated!
>
> With all my best regards!
>
> Yours sincerely
>
> Jingyun Zhang
>
>
>
>
>
>
>
>
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