Hello Dear all,
My doubt is quite simple (I think)...I am diagonalizing an Hermitian matrix (Hamiltonian) from which I need to get the eigenvectors to calculate the spin expectation as a function of some parameter that is changed in the Hamiltonian. The problem is that when I have a degeneracy in the eigenvalues the eigenvectors do not agree with the expected behavior (analitical), in fact it mixes the spin components in the eigenfunction wich is expected not to happen as the elements in the Hamiltonian are not mixing them. I am using the Zheev subroutine.
If anyone has faced this issue before or knows how to solve it, I will really appreciate!!!
thank you so much in advance!