Quantum Monte Carlo diagonalization with angular momentum projection

We present a description of the quantum Monte Carlo diagonalization method. This method has been introduced recently as an approach having both the advantage of the quantum Monte Carlo method and that of the direct diagonalization of the Hamiltonian matrix. In addition, the angular momentum projection is implemented so as to remove the degeneracy with regard to magnetic quantum number. We show that with this method the convergence of the eigenvalues is improved and that the wave functions of excited states can be obtained more easily. Moreover, the calculation of transition matrix elements becomes simpler.