Nonperturbative method for core–valence correlation in pseudopotential calculations: Application to the Rb2 and Cs2 molecules

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Abstract
The core–valence correlation is introduced into ab initio relativistic pseudopotential calculations by modifying the existing core polarization potential. The salient feature of the method presented here is the use of an l‐dependent cutoff parameter (which is related to spherical harmonic functions) for solving the multicenter integrals over the 1/r4 ‐ and r/r3 ‐type operators. The method is tested on the Rb2 and Cs2 molecules considered as two valence‐electron problems. Reliable results for the molecular spectroscopic constants (Re, Te, De, and ωe ) are obtained for the ground state and the lowest excited states. Deviation from the experimental values ranges from 0.05 to 0.1 Å for Re, seldom exceeds 2 cm−1 for ωe, and is of the order of 100 cm−1 for De for most of the excited states.