Håkon Emil Kristiansen

• Pedersen, Thomas Bondo; Kristiansen, Håkon Emil; Bodenstein, Tilmann; Kvaal, Simen & Schøyen, Øyvind Sigmundson (2021). Interpretation of Coupled-Cluster Many-Electron Dynamics in Terms of Stationary States. Journal of Chemical Theory and Computation.  ISSN 1549-9618.  17(1), s 388- 404 . doi: 10.1021/acs.jctc.0c00977 Full text in Research Archive. Show summary

  We demonstrate theoretically and numerically that laser-driven many-electron dynamics, as described by bivariational time-dependent coupled-cluster theory, may be analyzed in terms of stationary-state populations. Projectors heuristically defined from linear response theory and equation-of-motion coupled cluster theory are proposed for the calculation of stationary-state populations during interaction with laser pulses or other external forces, and conservation laws of the populations are discussed. Numerical tests of the proposed projectors, involving both linear and nonlinear optical processes for the He and Be atoms, and for the LiH, CH+, and LiF molecules, show that the laser-driven evolution of the stationary-state populations at the coupled-cluster singles-and-doubles (CCSD) level is very close to that obtained by ful configuration-interaction theory provided all stationary states actively participating in the dynamics are sufficiently well approximated. When double-excited states are important for the dynamics, the quality of the CCSD results deteriorate. Observing that populations computed from the linear-response projector may show spurious small-amplitude, high-frequency oscillations, the equation-of-motion projector emerges as the most promising approach to stationary-state populations.

• Kristiansen, Håkon Emil; Schøyen, Øyvind Sigmundson; Kvaal, Simen & Pedersen, Thomas Bondo (2020). Numerical stability of time-dependent coupled-cluster methods for many-electron dynamics in intense laser pulses. Journal of Chemical Physics.  ISSN 0021-9606.  152 . doi: 10.1063/1.5142276 Full text in Research Archive.

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• Kristiansen, Håkon Emil (2019). Numerical stability of time-dependent coupled-cluster methods for many-electron dynamics in intense laser pulses.
• Kristiansen, Håkon Emil (2019). Time-dependent coupled-cluster theory for atoms & molecules in intense laser fields.
• Kristiansen, Håkon Emil (2019). Time-dependent coupled-cluster theory for atoms and molecules in intense laser fields.

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