title: DFT research on the dehydroxylation reaction of pyrophyllite 1. First-principle molecular dynamics simulations.
abstract: The dehydroxylation of pyrophyllite involves the reaction of OH groups and elimination of water molecules through two possible mechanisms, one involving the bridging hydroxyl groups of an octahedral Al (3+) pair and the other two hydroxyl groups reacting across the dioctahedral vacancy. First-principles molecular dynamics simulations at the density functional theory level are used together with the metadynamics algorithm to explore the free-energy surface (FES) of the initial step of the dehydroxylation. We observe that the two possible dehydroxylation mechanisms yield similar activation energies at 0 K, but at high temperatures, the cross mechanism has lower free energy than that of the on-site one. The dehydroxylation process produces different semidehydroxylated intermediates that should be taken into account. The role of the temperature in favoring a dehydroxylation nonconcerted chain mechanism over another is here elucidated, and a novel competitive mechanism, which is assisted by the structural apical oxygens in the high-temperature regime, is proposed.
authors.affiliation: Laboratorio de Estudios Cristalográficos, Instituto Andaluz de Ciencias de la Tierra (CSIC), Universidad de Granada, Av. Fuentenueva s/n, Granada, Spain.
authors.forename: Esther
authors.initials: E
authors.lastname: Molina-Montes
authors.forename: Davide
authors.initials: D
authors.lastname: Donadio
authors.forename: Alfonso
authors.initials: A
authors.lastname: Hernández-Laguna
authors.forename: C Ignacio
authors.initials: CI
authors.lastname: Sainz-Díaz
authors.forename: Michele
authors.initials: M
authors.lastname: Parrinello