Full fourth-order MBPT calculations on the 3F, 3D and 1S states of the nickel atom with a Gaussian basis do not yield the correct non-relativistic energy ordering. Coupled-cluster single and double excitation calculations reveal a large discrepancy between fourth-order and infinite-order results. We achieve an improved separation of the states by employing a Slater basis and introducing infinite-order effects of triple excitations with our CCSD + T(CCSD) model.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry