Phonons (8): general equation in the harmonic approximation

New channel Vincent Meunier: title sample judged 'whole' (Nearly every upload is a structured physics lecture or worked tutorial (QM, thermo, DFT, phonons) with only a couple of ); passed a second screen for sellers/exam-prep/re-uploads; 0 of 3 sampled transcripts showed teaching, 0 not; titles picked one by one, checked strictly; oEmbed verified.