Determining Partial Atomic Charges for Liquid Water: Assessing Electronic Structure and Charge Models

Partial atomic charges provide an intuitive and efficient way to describe the charge distribution resulting intermolecular electrostatic interactions in liquid water. Many models exist it is unclear which model provides best assignment of partial response local molecular environment. In this work, we systematically scrutinize various electronic structure methods (Mulliken, natural population analysis, CHelpG, RESP, Hirshfeld, Iterative Bader) by evaluating their performance predicting dipole moments isolated water, water clusters, as well transfer dimer Although none seven capable fully capturing moment increase from (1.85 D) (about 2.9 D), Hirshfeld method performs for reproducing its experimental average moment, yielding a reasonable amount transfer, showing modest sensitivity The dependent on choice density functional quantum treatment computed generally increases with percentage exact Hartree-Fock exchange functional, whereas between molecules decreases. For including two full solvation shells surrounding (within about 5.5 A central water) chemical calculation converges molecule. Our final pragmatic charge-assigning protocol M06-HF/aug-cc-pVDZ region cutoff radius A.