Speeding-up Ab Initio Simulations: Novel Approaches for Extended Lagrangian Molecular Dynamics

Modern theoretical chemistry is prompted to give insight into ultrafast phenomena from an atomistic point-of-view and to give an interpretation of the experimental data from time-resolved spectroscopies. Ab initio molecular dynamics (AIMD) is the prominent approach to capture both electronic and nuclear relaxation events.¹ Among different approaches to molecular simulations, the Extended Lagrangian AIMD techniques appear to give best performances with respect to the accuracy/cost ratio. The fictitious electronic mass is a crucial parameter, because it has to ensure an efficient propagation of the electronic degrees of freedom, while keeping a strong degree of adiabaticity.² Current implementations are based on a uniform or an energy-based weighting of atom centered basis functions and often cannot capture their core or valence-like character. A novel mass weighting scheme, based upon a rational classification of the atomic functions, will be proven to be consistently more reliable, while avoiding errors typically occurring with fixed energy thresholds. Such an approach may allow larger time-steps, while ensuring a strong physical soundness to the simulation.

¹ Rega, N. et al. J. Phys. Chem. A 122.11 (2018): 2884.
² Iyengar, S., et al. J. Chem. Phys. 115.22 (2001): 10291.