Partial third-order quasiparticle theory: An application to the photoelectron spectrum of s-tetrazine

An alternative choice of reference state averages in electron propagator theory and retention of all self-energy terms through third-order gives rise to the partial third-order self-energy approximation, P3. Quasiparticle P3 calculations avoid the chief computational bottlenecks of third-order theory and the outer valence Green's function (OVGF). P3 requires no multiplicative factors for scaling self-energy terms and produces better accuracy than OVGF. An application to the photoelectron spectrum of s-tetrazine illustrates the ability of the P3 method to predict correct final state orderings. (C) 1997 John Wiley & Sons, Inc.