Achieving an Order of Magnitude Speed-up in Hybrid Functional and Plane Wave based Ab Initio Molecular Dynamics: Applications to Proton Transfer Reactions in Enzymes and in Solution.

Ab initio molecular dynamics (AIMD) with hybrid density functionals and plane wave basis is computationally expensive due to the high computational cost of exact exchange energy evaluation. Recently, we proposed a strategy to combine adaptively compressed exchange (ACE) operator formulation and multiple time step (MTS) integration scheme to reduce the computational cost significantly [J. Chem. Phys. 151, 151102 (2019)]. However, it was found that the construction of the ACE operator, which has to be done at least once in every MD time step, is computationally expensive. In the present work, systematic improvements are introduced to further speed-up by employing localized orbitals for the construction of the ACE operator. By this, we could achieve a computational speed-up of an order of magnitude for a periodic system containing 32-water molecules. Benchmark calculations were carried out to show the accuracy and efficiency of the method in predicting the structural and dynamical properties of bulk water. To demonstrate the applicability, computationally intensive free energy computations at the level of hybrid density functional theory were performed to investigate (a) methyl formate hydrolysis reaction in neutral aqueous medium and (b) proton transfer reaction within the active site residues of class-C $\beta$-lactamase enzyme.