Optimization with respect to the spinor basis

In analysing the variation of the energy functional with respect to orbital variations, we need to maintain the orthonormality of the spinor basis. It is convenient to do this by constructing a unitary transformation U = I -t- T such that the set p = 1. A/1 WqUqp is an improved basis. 

The way in which negative energy states have a habit of reappearing in the theory may seem paradoxical, even alarming, since our stated aim is to con- 

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