Projection Operators in Quantum-Mechanical Perturbation Theory
W. R. Salzman, M. E. Baur
The construction of operator functionals of the full Hamiltonian of a quantum-mechanical system which act as projection operators for a specified exact eigenstate is studied. In general these operator functionals are not equivalent to the formal operator |ψ〉〈ψ|, where |ψ〉 is the state of interest, and are not always idempotent. A formal method by which standard perturbation theoretic expansions for the exact ground-state vector and ground-state energy of the system can be recovered by expansion of a certain operator functional of this type is presented. Related work is briefly discussed.
The Journal of Chemical Physics•May 1, 1965•3 citations