Large component Gaussian 2-spinor basis functions

The l/REP(r), U ARKP(r), and terms At/f EP(r) in 11s0 of Eqs. (23), (31), and (34) or Eq. (6), respectively, are derived in the form of numerical functions consistent with the large components of Dirac spinors as calculated using the Dirac-Fock program of Desclaux (27). These operators have been used in their numerical form in applications to diatomic systems where basis sets of Slater-type functions are employed (39,42,43). It is often more convenient to represent the operators as expansions in exponential or Gaussian functions (32). The general form of an expansion involving M terms is... 

Strict relations exist between the two large components and the two small components, and these may be imposed directly, resulting in large and small component basis sets, and from Eq. [66]. These basis sets may then be used to describe the four-component spinors as they appear in Eq. [66]. A simpler procedure is to expand the spinors in four-component basis functions composed of ordinary Gaussian or Slater functions as follows ... 

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