This poster exhibits our recent work at the interface of electronic structure theory and nuclear dynamics/sampling. In particular, acceleration of ab initio molecular dynamics (AIMD) is attained via multiple-timestep (MTS) algorithms.On-the-fly, AIMD methods provide the ability to explore parameter-free potential energy surfaces for reactive chemistry. While significant progress has been made toward extending such methodology to large systems, these simulations remain a computationally demanding enterprise and are often many orders of magnitude more costly than their force field-based counterparts. This work presents a series of approaches that exploit the inherent spatial and temporal separability of under-the-hood electronic structure theory components for new dynamical simulations of large, reactive chemical systems. Importantly, none of these approaches follow the standard protocol of addressing the electronic structure algorithm alone; they are specifically tailored to dynamics and sampling. By exploiting separable pieces of the electronic structure theory innards, several MTS-AIMD protocols become available. Demonstrated algorithms include an SCF/Correlation multiple-timestep scheme, in which the HF and electron correlation components are updated on differing timescales. For density functional theory AIMD, an integral threshold-based approach is similarly implemented. Speedups in each case are on the order of 2-10. For larger systems, a many-body MTS-AIMD approach is developed, which addresses the non-linear scaling of most electronic structure methods. Finally, application of these methods to ionized water clusters, (H2O)n+, is presented. In this reactive, open-shell cation system, accurate electronic structure theory is critical for even a correct qualitative description. The proton-transfer and isomerization dynamics following ionization are tracked via AIMD. These simulations unequivocally demonstrate the propensity of the initially formed ion-radical contact pair (H3 O+?OH) to break apart and independently diffuse via Grotthuss proton-shuttling dynamics.

Multiple-timestep ab initio molecular dynamics

247th National Meeting (2014)

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