Ab initio computed interaction forces are employed to describe the microsolvation of the A+2(2Sigma) (A=Li, Na, K) molecular ion in 4He clusters of small variable size. The minimum energy structures are obtained by performing energy minimization based on a genetic algorithm approach. The symmetry features of the collocation of solvent adatoms around the dimeric cation are analyzed in detail, showing that the selective growth of small clusters around the two sides of the ion during the solvation process is a feature common to all three dopants.

The water-splitting process on electrochemical cells is studied with focus on the energetics of the oxygen evolution reaction at the TiO2-based anodes. New reaction mechanisms are proposed that lead to the decomposition of water molecules on TiO2 clusters. The oxygen evolution reaction at the anode is investigated using electronic structure calculations based on density functional theory (DFT). Simulations are carried out for different cluster sizes (monomers and dimers). For each reaction path, the free energy profile is computed, at different biases, from the DFT energies as well as the entropic and the zero-point energy contributions. The mechanisms of the oxygen evolution reaction explored in the present work are found to be energetically more feasible than alternative reaction pathways considered in previous theoretical works based on cluster approximations of the surface of the photocatalyst. Finally, the representation of the surface of specific, commonly occurring, titanium dioxide crystals (e.g., rutile and anatase) within the small cluster approximation is able to reproduce qualitatively the rutile (110) outperforming of the anatase (001) surface.

We investigate the influence of doping TiO2 surfaces with transition metals (TMs) on the performance of TiO2-based electrodes for the water-splitting electrochemical reaction. Two cluster models of the TM-doped active sites which resemble both the TiO2 anatase (001) and rutile (110) surfaces are considered for the evaluation of the water decomposition reaction when a Ti is replaced by a TM atom. These models constitute a direct extension from our previous work in which similar representations were employed to address the water-splitting reaction on pure TiO2-based electrodes. Regarding the cluster structure as a simplified representation of an active site on the anode in the electrochemical cell, the oxygen evolution reaction (OER) is investigated using density functional theory (DFT). Simulations are carried out for a set of TMs spanning from vanadium to nickel. The proposed reaction pathways are evaluated via the variation of the free-energy profile with respect to the applied external bias. The late TMs explored in this workFe, Co, and Niare found to reproduce the observed experimental trends for the overpotentials in TiO2 doped electrodes. In the case of Cr and Mn, the present study predicts an enhancement of the OER activity for the anatase-like clusters while a reduction of this activity is found for the rutile-like ones. Moreover, the vanadium-doped structures do not show relevant influence in the OER activity compared to pure TiO2-based cluster models.

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Cyclic and bent conjugated molecular systems have tunable optical, structural, and dynamical features that differentiate them from their linear counterparts. Examples of such systems are [n]­cycloparaphenylenes (CPPs), which consist of nanorings composed of n para-linked benzene units. Circular geometry and tunability of π-orbital overlaps and bending strains enrich them with unique physicochemical and electronic properties compared to those of the corresponding linear oligoparaphenylenes. Herein, we explore the changes of these properties on alkyl-tethered-p-heptaphenylenes by modifying the methylene tether lengths from 1 to 19 carbons, leading to a gradual linearization of the conjugated backbone conformation. For this purpose, the photoinduced internal conversion processes of different alkyl-tethered-p-heptaphenylenes are simulated using nonadiabatic excited-state molecular dynamics. We found that the greater the strain introduced on the conjugated system, the slower the electronic and vibrational energy relaxation process. All bent p-heptaphenylenes exhibit similar patterns of intramolecular energy redistribution that finally spatially localize the exciton on phenylene units in the middle of the conjugated chain. This behavior is opposite to the random exciton localization previously reported for [n]­CPPs. Moreover, the nonadiabatic S2 → S1 electronic transition activates specific collective asymmetric vibrational excitations that promote periodic oscillatory evolution of the excitonic wave function before an excessive energy dissipates into the bath degrees of freedom.