The complex scaled multiconfigurational time-dependent Hartree-Fock method for studying resonant states: application...

The complex scaled multiconfigurational time-dependent Hartree-Fock method (CMCTDHF also called the complex scaled multiconfigurational linear response method) is used to study the doubly excited He 2s(2) Feshbach resonance energy and lifetime. Various even-tempered Gaussian basis set/complete active space (CAS) combinations are examined. The results are compared with the complex scaled full configuration interaction (FCI) [P. R. Zdanska and N. Moiseyev, J. Chem. Phys. 123, 194105 (2005)], complex-scaled equation-of-motion coupled-cluster method with single and double substitutions [K. B. Bravaya, D. Z. Zuev, E. Epifanovsky, and A. I. Krylov, J. Chem. Phys. 138, 124106 (2013)], and exact numerical calculations [Y. K. Ho, Phys. Rev. A 23, 2137 (1981); E. Lindroth, Phys. Rev. A 49, 4473 (1994); A. Bürgers, D. Wintgren, and J.-M. Ross, J. Phys. B 28, 3163 (1995); and N. Elander, S. Levin, and E. Yarevsky, Phys. Rev. A 67, 062508 (2003)]. It is shown that CMCTDHF is able to provide highly accurate resonance parameters with a fairly small size of basis set and CAS, where the computational resources required are much less than the complex scaled FCI method and exact numerical results.