Dear all:
I have read the paper titled ??Theory of systematic absence of NaCl-type
(??-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 ?CZ2/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 ?? 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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