On the connection of the Independent-Pair Model with a variational principle

Abstract

It is shown thatBrenig's method of deriving the basic equations of the Independent-Pair Model can also be understood from a variational principle applied to the pseudoexpectation value 〈п¦H¦Ψ〉 (п=model wave function,Ψ=true wave function). Deviations from a vanishing first and second variation of 〈п¦H¦Ψ〉 with respect to the model wave functionп are shown to be due only to the independent-pair approximation, and thus permit us to make a qualitative estimate of the accuracy of this method.