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O: Fachverband Oberflächenphysik

O 36: Focus Session: Mineral-water interfaces II

O 36.2: Vortrag

Dienstag, 10. März 2026, 11:00–11:15, HSZ/0403

Ab initio exploration of water clusters on CaF₂ — •Isaac Azahel Ruiz Alvarado¹, Wolf Gero Schmidt¹, Paul Laubrock², Jonas Heggemann², and Philipp Rahe² — ¹Lehrstuhl für Theoretische Materialphysik, Universität Paderborn, Paderborn, Germany — ²Institut für Physik, Universität Osnabrück, Osnabrück, Germany

The electronic and structural properties of the CaF₂(111) surface-water interface are investigated from first-principles calculations. The energetic landscape for single molecular adsorption is calculated using standard DFT with London dispersion forces corrections. Single water molecules are found to preferentially adsorb on surface Ca atoms while large diffusion energy barriers are determined that restrict lateral movement of the water molecules. Additionally, the adsorption energies for the intact water molecule are compared to dissociative adsorption.

Multiple water molecules are included in the calculations to simulate the ice-like clusters observed experimentally by high-resolution AFM data acquired with CO-terminated tips. In order to understand the formation of these clusters, hexagonal rings similar to the ice I_h motif are modeled on top of the CaF₂ surface slab. The ice-surface incommensurability coupled with large diffusion barriers and preferred adsorption sites is suspected to limit the formation of a closed water monolayer. Complete water overlayers and additional structures are also calculated using molecular dynamics aided by machine learning force fields trained from ab initio calculations.

Keywords: Mineral-water interface; CaF2; Water adsorption; Density functional theory; Molecular dynamics