Dear all
What does it mean to have a horizontal line in the negative frequency regime of the phonon dispersion modes? I have a Li ion adsorbed at the surface of a heterostructure. The Li ion is at the saddle point. Actually I want to find the zero point energy of the Li ion. Should I consider the negative frequency of Li? or real? The image is attached.
Thank you for your cooperation.
Abdus Samad
Research associate at the University of Ulsan