[Pw_forum] harmonic instability and lattice constant

[karan deep]

Dear users

               i m studying the structural properties of some materials.
Interestingly i found that the lattice constant decrease with increase in
ionic radii of material in the cubic phase having harmonic instability
( negative frequency).

But no such odd behavior is found in the tetragonal phase of same
materials. Increase in ionic radii will result in higher lattice constant.

Are  the lattice constants found in phases having  negative frequencies
 correct or not

any help will be greatly appreciated.



Karandeep
Research Scholar
Physics Department,
IIT,  Delhi
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