Decisive role of nuclear quantum effects on surface mediated water dissociation at finite temperature

Abstract

Water molecules adsorbed on inorganic substrates play an important role in several technological applications. In the presence of light atoms in adsorbates, nuclear quantum effects (NQE) influence the structural stability and the dynamical properties of these systems. In this work, we explore the impact of NQE on the dissociation of water wires on stepped Pt(221) surfaces. By performing ab initio molecular dynamics simulations with van der Waals corrected density functional theory, we note that several competing minima for both intact and dissociated structures are accessible at finite temperatures, making it important to assess whether harmonic estimates of the quantum free energy are sufficient to determine the relative stability of the different states. We thus perform ab initio path integral molecular dynamics (PIMD) in order to calculate these contributions taking into account conformational entropy and anharmonicities at finite temperatures. We propose that when when adsorption is weak and NQE on the substrate are negligible, PIMD simulations can be performed through a simple partition of the system, resulting in considerable computational savings. We then calculate the full contribution of NQE to the free energies, including also anharmonic terms. We find that they result in an increase of up to 20% of the quantum contribution to the dissociation free energy compared to the harmonic estimates. We also find that the dissociation process has a negligible contribution from tunneling, but is dominated by ZPE, which can enhance the rate of dissociation by three orders of magnitude. Finally we highlight how both temperature and NQE indirectly impact dipoles and the redistribution of electron density, causing work function to changes of up to 0.4 eV with respect to static estimates. This quantitative determination of the change in work function provides a possible approach to determine experimentally the most stable configurations of water oligomers on the stepped surfaces.

i-PI 2.0: A universal force engine for advanced molecular simulations

“…• spatially localized ring polymer contraction (M. Rossi, M. Ceriotti) [29]; simple contraction scheme for weakly bound molecules, e.g. on surfaces;…”

“…As discussed in Ref. [29], the spatially localized ring polymer contraction (SL-RPC) is particularly useful when dealing with molecules weakly adsorbed on surfaces and can be seen as a simplified version of the adaptive multiresolution method [47]. In such cases, it is possible to seamlessly define a natural partition of the system into surface and adsorbates.…”

Perspective: Ring-polymer instanton theory

“…60,61 Techniques developed for increasing the efficiency of path-integral molecular dynamics could conceivably also be employed in instanton calculations. In particular, the use of higher-order discretization schemes 62 and ring-polymer contraction 63,64 has not yet been fully explored.…”

Measuring surface charge: Why experimental characterization and molecular modeling should be coupled

“…In addition to the potential speedup to be achieved with machine learning, the arrival of quantum computing may hold promise for drastically accelerating molecular simulations. Finally, advanced techniques capable of taking quantum nuclear effects into account are increasingly accessible [184,[198][199][200] and could help improving the description of water-based systems.…”