ONIOM approach for non-adiabatic on-the-fly molecular dynamics demonstrated for the backbone controlled Dewar valence isomerization

Non-adiabatic on-the-fly molecular dynamics (NA-O-MD) simulations require the electronic wave-function, energy gradients, and derivative coupling vectors in every timestep. Thus, they are commonly restricted to the excited state dynamics of molecules with up to approximate to 20 atoms. We discuss an approximation that combines the ONIOM(QM:QM) method with NA-O-MD simulations to allow calculations for larger molecules. As a proof of principle we present the excited state dynamics of a (6-4)-lesion containing dinucleotide (63 atoms), and especially the importance to include the confinement effects of the DNA backbone. The method is able to include electron correlation on a high level of theory and offers an attractive alternative to QM: MM approaches for moderate sized systems with unknown force fields. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4720090]