Résumé
This chapter proposes a new method based on a Jacobi-Wilson description of the system coupled to a modified Block-Davidson algorithm which provides eigenvalues and eigenvectors of selected highly excited vibrational states of polyatomic molecules. It shows that the Block-Davidson algorithm is efficient even when the state density is significant or when the intermode couplings are strong. The chapter also proposes some systematic ways to determine the Block of states used in the Block Davidson scheme.