Density functional theory calculations of nitrogen and oxygen equilibrium isotope fractionations in NO3−–NO2−–H2O aqueous system reveal inverse kinetic isotope effects during nitrite oxidation

Density Functional Theory Calculations of Equilibrium Mo Isotope Fractionation Factors among MoOxS4–x2– Species in the Aqueous Phase by the ONIOM Method

“…Previous research illustrated that solvent effects can influence the predicted α eq values. − The solute–solvent interactions include electrostatic forces, polarization, dispersion, repulsion, and intermolecular interactions . The implicit solvent model considers the electrostatic contribution, the sum of dispersion and repulsion energies, and the energy needed to create the solute cavity in the solvent .…”

“…The water-droplet or supermolecule explicit solvent method introduces solvent molecules to simulate a solution environment more realistically, which has been used to calculate β values of species in the aqueous phase. − We performed the water-droplet method on MoO 4 2– , MoS 4 2– , Na 2 MoO 4 , and Na 2 MoS 4 . The procedure is to add six water molecules to a system and optimize the structure repeatedly until the average β value converges.…”

“…The final β values were taken as the average of the last eight configurations (with 24 and 30 water molecules). More details of the water-droplet method can be found in our previous works. − …”

“…Density function theory (DFT) calculation combined with the Urey–Bigeleisen–Goeppert-Mayer (U–B–GM) model , is an efficient and reliable method to predict equilibrium isotope fractionation factors ( α eq ) due to its good predictions on harmonic vibrational frequencies. − Currently, only one study calculated the α eq values among MoO 4 2– , MoO 2 S 2 2– , and MoS 4 2– by isolated molecule models with the implicit solvent effect . Such practice may mismatch the observations in ocean water and laboratory experiments since the solvent molecules around the solute deeply influence the chemical behaviors of compounds. − To properly address the solvent effects in theoretical calculations, a hybrid-solvent model, which includes implicit and explicit solvent effects, as well as dispersion correction, is needed. Water-droplet − and periodic boundary condition (PBC) − methods are usually used to deal with aqueous phases with the consideration of explicit solvent molecules.…”

“…Such practice may mismatch the observations in ocean water and laboratory experiments since the solvent molecules around the solute deeply influence the chemical behaviors of compounds. − To properly address the solvent effects in theoretical calculations, a hybrid-solvent model, which includes implicit and explicit solvent effects, as well as dispersion correction, is needed. Water-droplet − and periodic boundary condition (PBC) − methods are usually used to deal with aqueous phases with the consideration of explicit solvent molecules. Nevertheless, such methods are labor-intensive and require large amounts of computational resources.…”