Relativistic Multiconfiguration Self-Consistent Field Theory

Relativistic Multiconfiguration Self-Consistent Field Theory 

The special importance of multiconfiguration SCF (MCSCF) methods in relativistic calculations was discussed in the introduction to this chapter. But quite apart from this, we know that MCSCF methods are very useful in nonrelativistic quantum chemistry, where various brands of the method, such as complete active space (CAS) SCF, 

The general MCSCF iteration starts with an orthonormal one-particle basis and a wave function calculated through a number of previous iterations (or from some suitable initial guess). If we assume that the process has completed iteration number k, the wave function at this stage may be written as The (optimal) MCSCF function is derived from this by means of orbital rotations in the one-electron basis and expansion in the set of A-electron states. In parametrized form we may write this as 

S is a normalization factor arising from the variation in the iV-particle space 

In line with what we have said previously, we must in general expect the orbital mixing coefficients Krs to be complex and the k matrices to be anti-Hermitian. In a Kramers-restricted formalism the operator must be invariant under time reversal, and we can incorporate this requirement by expressing the elements of k in terms of the operators  

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Relativistic Multiconfiguration Self-Consistent Field Theory... 

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