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 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 formulas are given for the second- and the third-order corrections. As a special case, the second-order Hamiltonian corresponding to an isolated electronic state is recovered which contains the coordinate-dependent mass-correction terms in the nuclear kinetic energy operator. For a multidimensional, explicitly coupled electronic band, the second-order Hamiltonian contains the usual Born–Oppenheimer terms and nonadiabatic corrections, but generalized mass-correction terms appear as well. These, earlier neglected terms, perturbatively account for the outlying (discrete and continuous) electronic states not included in the explicitly coupled electronic subspace.
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Research Article| July 03 2019
Effective non-adiabatic Hamiltonians for the quantum nuclear motion over coupled electronic states
Edit Mátyus ;
Edit Mátyus, Stefan Teufel; Effective non-adiabatic Hamiltonians for the quantum nuclear motion over coupled electronic states. J. Chem. Phys. 7 July 2019; 151 (1): 014113. https://doi.org/10.1063/1.5097899
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