15 votes

What does it mean to say a material is 'anharmonic'?

This is a difficult question without a straight-forward answer. In general you have to perform a test to decide whether the harmonic approximation is sufficient or whether you need to include higher ...
ProfM's user avatar
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12 votes
Accepted

What do phonon dispersion (or lattice dynamics) studies include?

TLDR: When you calculate phonons, you can describe electrons at different levels of theory, typically semilocal DFT, but also hybrids or dynamical mean-field theory. Phonons do include zero-point ...
ProfM's user avatar
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5 votes

Is there an upper limit of temperature after which the quasi-harmonic approximation (QHA) fails?

The starting point of most calculations is the Born-Oppenheimer approximation, which separates the electronic and nuclear degrees of freedom. The electronic structure problem is then solved using a ...
ProfM's user avatar
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4 votes

What does it mean to say a material is 'anharmonic'?

A "pure harmonic system" does not allow opportunity for evolution. It is the equivalent of a fixed point. In initial consideration, its stability seems appealing, as it appears to be a goal (...
MAAT's user avatar
  • 49

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