Excited states for molecules containing main group elements

Excited states for molecules containing main group elements 

As one of the main difficulties of the SOCI methods lies in the electronic correlation treatment, we choose an example with a large niunber of valence electrons to correlate, namely a di-halogen molecule, in order to illustrate how main-group pseudopotentials perform for spectroscopic constants. Moreover to test the ability of the various SOCI methods to handle accurately very large spin-orbit splittings, we deal with the heaviest experimentally known, the iodine molecule. 

Let us first consider ground state spectroscopic properties. Schwerdtfeger et al tested relativistic and correlation effects using a large-core (seven valence electrons) energy-consistent pseudopotential, with or without U ) 

Equilibrium distances re and dissociation energies D for the ground state of molecular iodine, from Ref. [97]. 

We first consider relativistic effects at the SCF step. The first two entries of Table 1 show the influence of the scalar relativity compared to U ), 

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