Critical Analysis of Ion--Water Interactions within Density Functional Theory and the Møller–Plesset Adiabatic Connection

The need for accurate models to describe the complex interplay of forces between ions and water across several thermodynamic conditions arises from the multitude of natural and industrial chemical phenomena in which hydrated ions participate. Accurately modeling ion–water systems has represented challenge to “workhorse” quantum chemical methods, such as Density Functional Theory (DFT) and Møller-Plesset perturbation theory (MPn), due to unsatisfactory accuracy, computational cost, or a combination of both. Recent advances in this direction include the development of data-driven many-body potentials that approximate the many-body expansion (MBE) from Density-Corrected DFT, aiming to mitigate delocalization errors in DFT through the evaluation of exchange-correlation functionals on Hartree-Fock densities. Nonetheless, DC-DFT studies of aqueous systems have thus far focused on systems with zero and ±1 charge. Given the recent identification of limiting cases for which the MBE of self-consistent and density-corrected functionals diverges for large F-(H2O)N clusters, a recent study points back to the exploration of efficient correlated wavefunction theory, which may provide a more reliable avenue.

In this talk, I will present a critical analysis of ion–water interactions in aqueous clusters, ranging from monatomic monovalent ions to molecular multivalent ions in water, within a variety of quantum chemical theories. Special attention is devoted to the recently introduced Møller-Plesset Adiabatic Connection (MPAC) functionals for non-covalent interactions. I place the predictive capabilities of MPAC theory into context with widely used quantum chemistry methods for ion–water interactions: DFT rungs 2-5, DC-DFT, and MP2 with respect to coupled cluster theory. Accuracy in predicting the interaction energy, and the MBE of MPAC functionals will be discussed, presenting MPAC as a promising cost-effective and pure electronic structure framework for ion chemistry.