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

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 E_ads, isosurface of the electron density difference, electrostatic potential, and the NCI plot. The E_ads 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 SOM_S with functional groups, including -OH, -COOH, -C=O, -SO- and pyridine, own the largest E_ads with X-mica, while the SOMs containing benzene ring have a stronger E_ads 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.