Microscopic Calculations of Nuclear Level Densities with the Extrapolated Lanczos Matrix (ELM) Method

A new method for computing the density of states in nuclei using an extrapolated form for the tri-diagonal matrix obtained from the Lanczos method is presented. This can be applied to configuration-interaction calculations with fully realistic nuclear Hamiltonians that are known to provide an excellent description of the low-lying structure of nuclei. This extrapolated Lanczos matrix (ELM) approach provides an accurate computation of the density of states up to the neutron separation energy for states that lie within the configuration space. Comparisons between theory and experiment for the average level spacings for p-wave resonances for iron isotopes using the 1p-0f-shell model space and realistic nuclear Hamiltonians are shown. Also we show results for J-dependence of the level density in ⁵⁷Fe, the total level density for negative-parity states in ⁵⁷Fe, and the level density for 2⁺ states in ⁵⁸Ni in comparison with experiment and with the stochastic method.