GRECP/5e-MRD-CI calculation of the electronic structure of PbH

The correlation calculation of the electronic structure of PbH is carried out with the Generalized Relativistic Effective Core Potential (GRECP) and MultiReference single- and Double-excitation Configuration Interaction (MRD-CI) methods. The 22-electron GRECP for Pb is used and the outer core 5s, 5p and 5d pseudospinors are frozen using the level-shift technique, so only five external electrons of PbH are correlated. A new configuration selection scheme with respect to the relativistic multireference states is employed in the framework of the MRD-CI method. The [6,4,3,2] correlation spin-orbit basis set is optimized in the coupled cluster calculations on the Pb atom using a recently proposed procedure, in which functions in the spin-orbital basis set are generated from calculations of different ionic states of the Pb atom and those functions are considered optimal which provide the stationary point for some energy functional. Spectroscopic constants for the two lowest-lying electronic states of PbH ($^2\Pi_{1/2}, ^2\Pi_{3/2}$) are found to be in good agreement with the experimental data.