15 votes

On the nature of zero-point energy (ZPE)

In the Born-Oppenheimer approximation nuclei are assumed to behave as classical point-like particles. However, in reality the wave-particle duality also applies to them, and so the Schrödinger ...
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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 ...
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5 votes

Supercell model for a disordered system in phonon calculations using the harmonic approximation

If you have a system without periodicity like your disordered solid solution, then you should use a $1\times1\times1$ $\mathbf{q}$-point grid for a phonon calculation (equivalent to a $1\times1\times1$...
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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 (...
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3 votes

On the nature of zero-point energy (ZPE)

The Born-Oppenheimer (BO) approximation works well at high temperatures (far from 0 K), but the quantum nature of the nuclei (i.e. the zero-point energy) is an important consideration at low ...
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