Relativistic Pseudopotential Calculations for Electronic Excited States

Relativistic Pseudopotential Calculations for Electronic Excited States 

Christian Teichteil, Laurent Maron and Valerie Vallet 

route de Narbonne, 31062 Toulouse cedex, France Electronic-mail christian.teichteil( irsamc.ups-tlse.fr 

Relativistic and electron correlation effects play an important role in the electronic structure of molecules containing heavy elements (main group elements, transition metals, lanthanide and actinide complexes). It is therefore mandatory to account for them in quantum mechanical methods used in theoretical chemistry, when investigating for instance the properties of heavy atoms and molecules in their excited electronic states. In this chapter we introduce the present state-of-the-art ab initio spin-orbit configuration interaction methods for relativistic electronic structure calculations. These include the various types of relativistic effective core potentials in the scalar relativistic approximation, and several methods to treat electron correlation effects and spin-orbit coupling. We discuss a selection of recent applications on the spectroscopy of gas-phase molecules and on embedded molecules in a crystal enviromnent to outline the degree of maturity of quantum chemistry methods. This also illustrates the necessity for a strong interplay between theory and experiment. 

In the frame of ab initio methods, much attention was paid in the last decades to the fields of relativity and correlation. Relativistic approximations have been defined in all-electron schemes [1] able to handle correlation, even using sophisticated Cl methods. Unfortunately such methods are very computer resource demanding, and are therefore severely limited to systems containing at most two heavy atoms. Three ingredients can be employed, separately or altogether to improve the efficiency in the calculations  

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