Coupled-cluster calculations of matrix elements and ionization energies of low-lying states in sodium

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Abstract
Accurate nonrelativistic calculations of ionization energies and hyperfine structures for the 3s and the 3p states, and of the dipole transition 3s-3p, are presented for Na, using wave functions obtained in the coupled-cluster approach including single and double excitations (CCSD). Agreement with experimental results is at the percent level, corresponding to an error in the correlation contribution of approximately 5%. Certain three-body cluster contributions to the 3s ionization energy and the 3s hyperfine structure are evaluated and are found to account for the main part of the discrepancies between the values obtained from CCSD calculations and the experimental results.