Nuclear velocity perturbation theory for vibrational circular dichroism: An approach based on the exact factorization
Arne Scherrer1, Federica Agostini2, Daniel Sebastiani1
1Martin-Luther-University Halle-Wittenberg, von-Danckelmann-Platz 4, D-06120 Halle, Germany.
Abstract:
The nuclear velocity perturbation theory (NVPT) for vibrational circular dichroism (VCD) is derived from the exact factorization of the electron-nuclear wave function. This new formalism offers an exact starting point to include correction terms to the Born-Oppenheimer (BO) form of the molecular wave function, similar to the complete-adiabatic approximation. The corrections depend on a small parameter that, in a classical treatment of the nuclei, is identified as the nuclear velocity. Apart from proposing a rigorous basis for the NVPT, we show that the rotational strengths, related to the intensity of the VCD signal, contain a new contribution beyond-BO that can be evaluated with the NVPT and that only arises when the exact factorization approach is employed. Numerical results are presented for chiral and non-chiral systems to test the validity of the approach.
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