Novel extrapolation method in the Monte Carlo shell model

We propose an extrapolation method utilizing energy variance in the Monte Carlo shell model to estimate the energy eigenvalue and observables accurately. We derive a formula for the energy variance with deformed Slater determinants, which enables us to calculate the energy variance efficiently. The feasibility of the method is demonstrated for the full pf-shell calculation of Ni-56, and the applicability of the method to a system beyond the current limit of exact diagonalization is shown for the pf + g(9/2)-shell calculation of Ge-64.