THE FEENBERG SERIES - AN ALTERNATIVE TO THE MOLLER-PLESSET SERIES

The Feenberg series is reintroduced as a perturbation series with improved convergence characteristics for quantum-chemistry calculations. It is defined through a scaling of H0, the parameter being defined such that the third-order correction is zero. The Feenberg series is suggested as an improvement to the Moller-Plesset series, the fourth-order energy being trivially obtained in terms of MP2, MP3 and MP4 energies. Benchmark studies are reported, where it is found that if MP3 < 0, then the Feenberg fourth-order energy is better than the MP energy at fifth order, and if MP3 > 0, the perturbation series is smoothed.