First-principles Molecular Dynamics maps out complete mineral surface acidity landscape

Abstract

In "Interfacial structures and acidity constants (pKa) {{editor, shouldn' the a be a subscript?}} of goethite from first principles molecular dynamics siluations," authors Y. Zang, X. Lui, J. Cheng, and X. Lu (Zhang et al. 2021) apply First Principles molecular dynamics (FPMD, also called Density Functional Theory MD, DFT/MD, or ab initio MD, AIMD) to evaluate the complete set of acidy constants (pKa) of the hydroxyl groups on the most prominent goethite crystal facets. The pKa of these OH and OH+ (Sprik 2000) groups are compared with available data from the multisite complexation (MUSIC) model traditionally used to estimate pKa on mineral surfaces. The authors have presented eloquent rational for the importance and implications of understanding goethite acidity constants in room temperature geochemistry settings. Here I focus on the computational aspects, the strengthes of FPMD, and its possibilities. pK calculations represent a significant triumph of the FPMD free energy formulation. Many FPMD simulations in the literature are conducted in a non-equilibrium mode and are "numerical This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America. The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

Surface Acidity and As(V) Complexation of Iron Oxyhydroxides: Insights from First-Principles Molecular Dynamics Simulations

“…Possible reactive sites for cations and anions on different surfaces can be derived based on the calculated p K a s (Table ). The sites bearing net negative charges in the normal pH range are considered to be reactive for cations and the sites with coordinated water that can be replaced with anions are considered to be reactive for anions. , It can be found that the lepidocrocite (010) surface has no reactive sites and therefore is inert. Singly coordinated sites contribute to most of the reactivities and are reactive on all surfaces.…”

Adsorption at Nanoconfined Solid–Water Interfaces

“…The effect of nanoconfinement on the pK a of surface OH groups has been challenging to compute with first-principles calculations. The deprotonation free energies can be computed using AIMD PMF simulations and related to the pK a of the surface OH groups (130). However, due to the computational cost, AIMD simulation cell sizes are generally limited to a thickness of water region of <2 nm; confinement effects await future quantification.…”