The classical molecular dynamics calculations were carried out using Tinker v8.1. Each 14.27 Å 3 simulation cell contained 96 solvent H 2 O molecules and one solute molecule (H 2 O, NH 3 , or NH + 4 ) that was constrained to remain at the center of the cell throughout the dynamics. The geometries were optimized at 0 K before a 10 ps (∆t = 1 fs) simulation to heat the system up to 300 K using the Nosé-Hoover thermostat within the NVT ensemble. Production runs were then carried out for 1 ns under these same conditions. All quantum chemistry calculations were performed with a development version of the Q-Chem 5.4 software package. Density functional calculations utilized a dense grid containing 99 radial points treated under the Euler-Maclaurin scheme and 590 angular points using a Lebedev quadrature for the evaluation of the exchange-correlation potential. All DFT calculations employ the exact two-component X2C Hamiltonian to self-consistently account for scalar relativistic effects. The EA-TDDFT calculations used the rCAM-B3LYP functional, which has been established to perform well for XAS, whereas standard TDDFT calculations employed the SRC1-R1 functional that was specifically optimized for XAS with TDDFT. A mixed basis set was employed in all calculations using aug-pcX-2 for the central solute atom, pcseg-1 for all H atoms, and the doubly-augmented d-aug-pcseg-1 basis set for all solvent O atoms. Double-augmentation of aug-pcseg-1 was obtained through a simple geometric sequence protocol. All computed spectra were broadened to obtain a full-width at halfmaximum of 0.4 eV in accordance with Ref. 22.