Shifting the pole of the energy denominators from the real axis to the imaginary results in a damping of the equation in degenerate cases. The term-by-term absolute value of the expression provides a simple and useful formula to treat quasidegenerate problems. The power of the new expression is illustrated on several examples calculating the correlation energy of some molecules. The Møller-Plesset results are scarcely affected by the proposed modification in normal cases but significant improvement is observed in quasidegenerate situations. The proposed formula is size consistent and its evaluation does not need extra computational effort.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry