A multi-reference equation of motion method in nuclear structure calculation

Static correlations in atomic nuclei are responsible for nuclear deformation. Capturing these correlations in nuclear structure and decay computations has been challenging. For example, excited intermediate states are required to calculate the nuclear matrix element (NME) for the two-neutrino double beta decay. However, some of these states are dominated by intruder configurations, and conventional methods of constructing valence effective interactions inside a model space fail. We present a new method of capturing these correlations. First, the low-lying states are computed using the VS-IMSRG method within the model space. Secondly, states that are dominated by intruder components are produced by exciting the system from the model space to the excluded space using the equation of motion (EOM) method. We applied this multiple reference EOM method to light mass nuclei to compute their two-neutrino double beta decay NMEs.