Ab initio Monte Carlo shell model calculations for ⁷Li and ⁹Li low-lying spectra

The low-lying spectra of ⁷Li and ⁹Li are investigated within an ab initio Monte Carlo Shell Model (MCSM) employing a realistic potential obtained via the Unitary Correlation Operator Method (UCOM). The MCSM calculations in a 4-major-shells model space for the binding energy and mass quadrupole moment of ^7,9Li show good convergence when the MCSM dimension reaches 20. The excitation energy of the J^π = 1/2^- state for ⁷Li and the magnetic moments for ^7,9Li ground states in the MCSM with a treatment of spurious center-of-mass motion are close to the experimental data. Correct level ordering of J^π = 3/2^- and 1/2^- states for ^7,9Li can be reproduced due to the inclusion of three-body correlations in the MCSM + UCOM. However, the excitation energy of J^π = 1/2^- state for ⁹Li is not reproduced in the MCSM mainly due to the lack of larger model space. (author)