Effective non-adiabatic Hamiltonians for the quantum nuclear motion over coupled electronic states.

@article{Mtyus2019EffectiveNH,
  title={Effective non-adiabatic Hamiltonians for the quantum nuclear motion over coupled electronic states.},
  author={Edit M{\'a}tyus and Stefan Teufel},
  journal={The Journal of chemical physics},
  year={2019},
  volume={151 1},
  pages={
          014113
        }
}
The quantum mechanical motion of the atomic nuclei is considered over a single- or a multidimensional subspace of electronic states which is separated by a gap from the rest of the electronic spectrum over the relevant range of nuclear configurations. The electron-nucleus Hamiltonian is block-diagonalized up to O(εn+1) through a unitary transformation of the electronic subspace, and the corresponding nth-order effective Hamiltonian is derived for the quantum nuclear motion. Explicit but general… 

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