Interactions between typical functional groups of soil organic matter and mica (001) surface: A DFT study

Abstract

In this study, the interactions between mica and soil organic matters (SOMs) are investigated by the density functional theory (DFT) calculations. The adsorption behavior of 12 typical SOMs on X-mica (X = Na, K or Cs) are systematically studied based on 96 interaction models. Three typical adsorption configurations for each SOMs are considered. The interactions details are explored by the further analysis of Eads, isosurface of the electron density difference, electrostatic potential, and the NCI plot. The Eads between mica and SOMs is proved strong for Na-mica due to the smallest ionic radius of Na. For example, it is 0.78 eV. 0.48 eV, 0.27 eV for CH4O/Na-mica, K-mica and Cs-mica respectively. The SOMS with functional groups, including -OH, -COOH, -C=O, -SO- and pyridine, own the largest Eads with X-mica, while the SOMs containing benzene ring have a stronger Eads than that of the hydrocarbon alkyl. The Light Gradient Boosting Machine (LGBM) method is used to analyses the importance of the different factors in regulating the SOMs/X-mica interactions. The electronegativity and ionic radius of cations in X-mica are found to be the most important factors, followed by the configurations and functional groups of SOMs. This work provides a detailed DFT based method for SOM/minerals interactions which provide deep understanding on effects of SOM in the mineral morphogenetic transformation.