Ab initio study of water dissociation on a charged Pd(111) surface

Interactions between molecules and electrode surfaces play a key role in electrochemical processes and are a subject of extensive research, both experimental and theoretical. In this manuscript, we address the water dissociation reaction on a Pd(111) electrode surface, modelled as a slab embedded in an external electric field. We aim at unraveling the relationship between surface charge and zero-point-energy in aiding or hindering this reaction. We calculate energy barriers with dispersion-corrected density-functional theory and an efficient parallel implementation of the nudged-elastic-band method. We show that the lowest dissociation barrier, and consequently highest reaction rate, takes place when the field reaches a strength that induces a geometric frustration of the water molecule adsorbed on the surface. Zero-point energy contributions to the this reaction, on the other hand, remain nearly constant across a wide range of electric field strengths, despite significant changes in the reactant state

Quantum Nuclei at Weakly Bonded Interfaces: The Case of Cyclohexane on Rh(111)

The electronic properties of interfaces can depend on their isotopic constitution. One known case is that of cyclohexane physisorbed on Rh(111), in which isotope effects have been measured on the work function change and desorption energies. These effects can only be captured by calculations including nuclear quantum effects (NQE). In this paper, this interface is addressed employing dispersion‐inclusive density‐functional theory coupled to a quasi‐harmonic (QH) approximation for NQE, as well as to fully anharmonic ab initio path integral molecular dynamics (PIMD). The QH approximation is able to capture that deuterated cyclohexane has a smaller adsorption energy and lies about 0.01 Å farther from the Rh(111) surface than its isotopologue, which can be correlated to the isotope effect in the work function change. An investigation of the validity of the QH approximation relying on PIMD simulations, leads to the conclusion that although this interface is highly impacted by anharmonic quantum fluctuations in the molecular layer and at bonding sites, these anharmonic contributions play a minor role when analyzing isotope effects at low temperatures. Nevertheless, anharmonic quantum fluctuations cause an increase in the distance between the molecular layer and Rh(111), a consequent smaller overall work function change, and intricate changes in orbital hybridization

Ab initio study of water dissociation on a charged Pd(111) surface

Interactions between molecules and electrode surfaces play a key role inelectrochemical processes and are a subject of extensive research, bothexperimental and theoretical. In this manuscript, we address the waterdissociation reaction on a Pd(111) electrode surface, modelled as a slabembedded in an external electric field. We aim at unraveling the relationshipbetween surface charge and zero-point-energy in aiding or hindering thisreaction. We calculate energy barriers with dispersion-correcteddensity-functional theory and an efficient parallel implementation of thenudged-elastic-band method. We show that the lowest dissociation barrier, andconsequently highest reaction rate, takes place when the field reaches astrength that induces a geometric frustration of the water molecule adsorbed onthe surface. Zero-point energy contributions to the this reaction, on the otherhand, remain nearly constant across a wide range of electric field strengths,despite significant changes in the reactant state.<br