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

I can't seem to articulate what made me ask this question but it sprang up when I asked: What does it mean to say a material is 'anharmonic'?.

I've heard before that the electronic entropy becomes a force to reckon at extreme (near melting) temperatures since electrons acquire tremendous energy at such temperatures. Does the failure of the QHA have something to do with this? I don't as such understand the physical meaning (rather the implication) of 'coupling' but is electron-phonon coupling the demise of QHA? Also, does phonon-phonon coupling have any role to play here?