Automated Parametrization Approach for Coarse-Graining Soil Organic Matter Molecules

Area of Science:

• Environmental Science
• Computational Chemistry
• Soil Science

Background:

• Soil organic matter (SOM) molecular structure and interactions are crucial for ecological functions.
• The complexity and heterogeneity of SOM pose significant challenges for systematic study.
• Atomistic simulations offer a complementary approach to experimental methods for understanding SOM at the molecular level.

Purpose of the Study:

• To develop a parametrization strategy for converting atomistic soil organic matter models into a coarse-grained representation.
• To enable the exploration of larger time and length scales in SOM simulations.
• To directly construct and analyze coarse-grained SOM models with diverse compositions.

Main Methods:

• Utilized the Vienna Soil Organic Matter Modeler 2 (VSOMM2) for initial SOM model construction.
• Developed a parametrization strategy for coarse-graining VSOMM2-generated atomistic structures.
• Employed a conformer search technique for direct construction of coarse-grained models.
• Performed molecular dynamics simulations on coarse-grained models.
• Analyzed density and potential energy profiles of the models.

Main Results:

• Successfully created coarse-grained SOM models based on International Humic Substances Society samples.
• Demonstrated that electrostatic interactions are the primary drivers of structural packing in SOM.
• Observed a local phase separation process, including the formation of SOM voids, over microsecond timescales.
• Found a partial correlation between SOM composition and calculated properties.

Conclusions:

• The developed coarse-graining technique significantly enhances the ability to simulate SOM at larger scales.
• This method facilitates direct analysis of SOM models without the need for computationally expensive atomistic simulations.
• The findings highlight the importance of electrostatic forces and reveal dynamic processes like phase separation in SOM structure.