[QE-users] Visualizing Phonon Modes

[Paolo Giannozzi]

On 24/08/2022 16:55, Baer, Bradly via users wrote:

> For example modes 1-3 do not look like TA/LA modes and are pointing
> in diagonal directions rather than being aligned with the axes

For degenerate eigenvalues, the numerical diagonalization yields an 
arbitrary linear combination of eigenvectors spanning the degenerate 
subspace. So for the three TA/LA zero-frequency modes at Gamma, you get 
three translations along three arbitrary (but orthonormal) directions, 
not along the crystal or cartesian axis

Paolo
-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222