Hybrid schemes for the calculation of low-energy levels of shell model Hamiltonians

We investigate the use of hybrid schemes for the calculation of low-energy eigenstates of shell model Hamiltonians. These schemes mix the basic ideas behind the quantum Monte Carlo diagonalization (QMCD) method and the VAMPIR method. In applications to some fp nuclei using the GXPF1 effective Hamiltonian, we find most practical and time saving the use gradient methods (typical of the VAMPIR approach) with QMCD trial wavefunctions, which are Slater determinants for fp nuclei. We find that the number of many-body states needed to reach reasonable values of the ground-state energies for a given angular momentum is small. We also explore the possibility of using these hybrid methods for model Hamiltonians with a strong repulsive core.