Enabling Large-Scale Isobaric-Isothermal Hybrid Density Functional Theory Simulations in the Condensed Phase

The combination of ab initio molecular dynamics (AIMD) and high-performance computing (HPC) has the potential to furnish an atomistic-level understanding of complex condensed-phase systems such as molecular liquids and crystals. Such a detailed understanding requires an accurate treatment of both the quantum mechanical interactions and statistical mechanical sampling under realistic experimental conditions (e.g., in the isobaric-isothermal (NpT) ensemble). However, the routine use of sophisticated quantum mechanical methods like dispersion-inclusive hybrid density functional theory (DFT) is hindered by the cubic-scaling cost of conventional reciprocal-space based approaches. With the use of localized occupied orbitals, we have developed a formally exact and linear-scaling algorithm that directly addresses this prohibitive cost. In this work, we derive and implement the exact-exchange contributions to the stress tensor, thereby enabling hybrid DFT-based AIMD simulations of arbitrary cell sizes and shapes in the NpT ensemble. As an application of this method, we will discuss the pyridine molecular crystal.

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