Influence of the Unique-Parity States on Collectivity ofLow-Lying States

The importance of the unique-parity single particle level in the description of nuclear collectivity is stressed in the framework of the nucleon-pair shell model truncated to the SD subspace. It is found that with the shell model Hamiltonian which includes the single particle energy term, the unique-parity single particle level has to be included for describing the low-lying collective states reasonably.