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 $\mathit{pf}$-shell calculation of ${}^{56}\mathrm{Ni}$, and the applicability of the method to a system beyond the current limit of exact diagonalization is shown for the $\mathit{pf}+g_{9/2}$-shell calculation of ${}^{64}\mathrm{Ge}$.

• Received 3 November 2010

DOI:https://doi.org/10.1103/PhysRevC.82.061305