Ionization energies in solution with the QM:QM approach

Abstract

Fragment-based QM:QM technique provides an efficient and accurate way for calculating energetics of vertical processes such as ionization.

Solvation energies of ions with ensemble cluster-continuum approach

“…F À ) and in these cases, the calculations on the ensemble of structures need to be conducted differently, for example using Koopmans' theorem, 79 the Maximum Overlap Method (MOM), 80 ionization as excitation method or QM:QM approach. 11 Finally, we need to sample the cluster structures. This can typically not be done at the same level of theory we use for the energy calculations which leads to further inconsistencies (see Fig.…”

“…While the first problem can be mitigated with various approaches, e.g. using fragmentation schemes such as QM/MM 10 or QM:QM 11 or linear scaling methods, [12][13][14] the second problem remains. Yet various attempts have been made to access single-ion solvation free energies via MD simulations, [15][16][17][18][19][20][21] including studies using polarizable models.…”

Probing Interfacial Effects on Ionization Energies: The Surprising Banality of Anion-Water Hydrogen Bonding at the Air/Water Interface

“…82,83,87 Long-range polarization does change dramatically upon ionization, however, leading to very slow convergence of VIEs with respect to the number of explicit water molecules. [87][88][89][90][91][92][93][94] Consideration of the Born ion model suggests ∼ R −1 convergence behavior, for an ion-water cluster of radius R, and in practice that may mean 500-1000 water molecules to obtain converged results. [88][89][90][91][92][93][94] This problem is not unique to VIEs and is also encountered in pK a calculations.…”

“…[87][88][89][90][91][92][93][94] Consideration of the Born ion model suggests ∼ R −1 convergence behavior, for an ion-water cluster of radius R, and in practice that may mean 500-1000 water molecules to obtain converged results. [88][89][90][91][92][93][94] This problem is not unique to VIEs and is also encountered in pK a calculations. 104 A solution to this conundrum is to use continuum boundary conditions to accelerate convergence with respect to the size of the atomistic solvent cluster.…”

“…That issue is examined here by computing bulk and interfacial VIEs for 16 common inorganic ions for which experimental data (from liquid microjets) are available, 59,86 using a combination of MD simulations and electronic structure calculations. Long-range polarization makes a significant contribution to VIEs in water, [87][88][89][90][91][92][93][94][95] and we incorporate this effect via dielectric continuum boundary conditions around an electronic structure calculation that includes several solvation shells of explicit water molecules. 95 Excellent agreement with experimental results suggests that our procedure constitutes a useful, general approach for modeling aqueous VIEs.…”