{\it Ab initio} studies of electron correlation and Gaunt interaction   effects in boron isoelectronic sequence using coupled-cluster theory
  In this paper, we have studied electron correlation and Gaunt interaction effects in ionization potentials (IPs) and hyperfine constants A of 2p$^2P_{1/2}$ and 2p$^2P_{3/2}$ states along with the fine structure splitting (FSS) between them for boron isoelectronic sequence using relativistic coupled-cluster (RCC) method. The range of atomic number Z has been taken from 8 to 21. Gaunt contributions are presented at both Dirac-Fock (DF) and coupled-cluster (CC) levels of calculations. The Gaunt corrected correlated results of the IPs and the FSS are compared with the results of NIST. Important correlation contributions like core correlation, core polarisation, pair correlation etc. are studied for hyperfine constants A. Many distinct features of correlation and relativistic effects are observed in these studies. With best of our knowledge, within Gaunt limit, most of the hyperfine constants are presented for the first time in the literature. 
Narendra Nath Dutta and Sonjoy Majumder
physics.atom-ph