2024/02/17 by Mads Greisen Højlund, Højlund, Mads Greisen, Ove Christiansen +1
Agricultural and Biological Sciences · Psychology · #Advanced Scientific Research Methods #Chemical Physics (physics.chem-ph) #Color perception and design #FOS: Physical sciences
paper · pdf · doi:10.48550/arxiv.2402.11378
openalex publication_date 2024/02/17 · openalex created_date 2024/02/22 · openalex updated_date 2026/07/28
We propose a new formulation of time-dependent coupled cluster with adaptive basis functions and division of the one-particle space into active and secondary subspaces. The formalism is fully bivariational in the sense of a real-valued time-dependent bivariational principle and converges to the complete-active-space solution, a property that is obtained by the use of biorthogonal basis functions. A key and distinguishing feature of the theory is that the active bra and ket functions span the same space by construction. This ensures numerical stability and is achieved by employing a split unitary/non-unitary basis set transformation: The unitary part changes the active space itself, while the non-unitary part transforms the active basis. The formulation covers vibrational as well as electron dynamics. Detailed equations of motion are derived and implemented in the context of vibrational dynamics, and the numerical behavior is studied and compared to related methods.