Approximate Hamiltonians from a Linear Vibronic Coupling Model for Solution-Phase Spin Dynamics.

The linear vibronic coupling (LVC) model is an approach for approximating how a molecular Hamiltonian changes in response to small changes in molecular geometry. The LVC framework thus has the ability to approximate molecular Hamiltonians at low computational expense but with quality approaching multiconfigurational calculations, when the change in geometry compared to the reference calculation used to parametrize it is small. Here, we show how the LVC approach can be used to project approximate spin Hamiltonians of a solvated lanthanide complex along a room-temperature molecular dynamics trajectory. As expected, the LVC approximation is less accurate as the geometry diverges from that at which the model was parametrized. We examine the accuracy of the predicted Hamiltonians by performing time-dependent quantum simulations of the spin dynamics of the molecule, with reference to the dynamics obtained using spin Hamiltonians projected from calculations at each step. We find that quantitatively accurate behavior is obtained when LVC parametrizations are performed at least every 10 fs during the trajectory.