“…Now, the fact that h enters in the off-diagonal elements of both matrices means that we can apply a previously used trick to reformulate the problem. 31,32 By transferring the off-diagonal elements of S to the left-hand side, the generalized eigenvalue problem H 0 · c n, k = E n, k S · c n, k is transformed into a standard one, h 0 · c n, k = ε n, k c n, k , with the relations…”