Novel computational chemistry infrastructure for simulating astatide in water: From basis sets to force fields using particle swarm optimization

Using the example of astatine, the heaviest naturally occurring halogen whose isotope At-211 has promising medical applications, we propose a new infrastructure for large-scale computational models of heavy elements with strong relativistic effects. In particular, we focus on developing an accurate force field for At- in water based on reliable relativistic DFT calculations. To ensure such calculations' reliability, we design novel basis sets for relativistic DFT, using the particle swarm optimization algorithm to optimize the exponents in the basis sets, and extending the idea of a polarization-consistent basis set to heavy elements. The resulting basis sets enable the well-grounded evaluation of relativistic DFT against "gold-standard'' CCSD(T) results. Accounting for strong relativistic effects, including spin-orbit interaction, via our redesigned infrastructure, we elucidate a noticeable dissimilarity between At- and I- in halide-water force field parameters, radial distribution functions, diffusion coefficients, and hydration energies. This work establishes the framework for the systematic development of polarization-consistent basis sets for relativistic DFT and accurate force fields for molecular dynamics simulations to be used in large-scale models of complex molecular systems with the elements from the bottom of the periodic table, including actinides and even superheavy elements.