Monte-Carlo calculations ind-s shell space have been done using two-body random interactions, to obtain ensemble-averagem-particle scalar moments up to fourth order. A shift of the spectrum shape from semi-circle to Gaussian with respect to the increase in number of particles can be clearly seen in terms of the ensemble-averaged fourth moment.

We obtain an expression for the ensemble-averaged moments inm-particle space of 2-body random Hamiltonians with same non-zero mean for the matrix elements, in the limit ofN → ∞,m ≫ 2. The eigenvalue density function can then be immediately obtained in terms of the eigenvalue density (a Gaussian whenm ≫ 2) for zero mean ensembles. The results of Monte-Carlo calculations for iso-scalar rotationally invariant 2-body ensembles have also been given.

A new derivation of the inverse energy-weighted sum-rules is given by applying the spectral distribution methods to the Rayleigh-Schrodinger perturbation theory. The scalar space result is then extended to the configurations. This is applied to obtain corrections to the ground-state energy estimates when the effective interaction is approximated by a model Hamiltonian obtained by taking linear combinations of various parts of the pairing and the Q.Q operators.