Thus, the operator (15) induces particle-hole (p-h) excitations with respect to the reference. In general, \( T \) generates up to \( Ap-Ah \) excitations, and the unknown parameters are the cluster amplitides \( t_i^a \), \( t_{ij}^{ab} \), ..., \( t_{i_1,\ldots,i_A}^{a_1,\ldots,a_A} \).