SilicaSolv: A Python package for simulation of hydrolysis of polysilicic acids

Zeolites are crystal porous materials composed by TO4 (T=Si, Al, Ga, B, etc.) tetrahedrals, widely used in many fields of industrial significance, such as catalysis, separation, and ion adsorption, etc. The hydrothermal synthesis of zeolite involves cascade condensation and hydrolysis of the precursors of TO4 in forms of orthosilicic acid, polysilicic acids and their anions, their solvation and ionization in the reaction mixtures for the formation and evolution of secondary and composite building unites, and their integration into zeolite crystallites, where the condensation and hydrolysis of polysilicic acids are crucial. In this study, a theoretical approach was developed and implemented in SilicaSolv to investigate the hydrolysis of the polysilicic acid. In this approach, the structure of a polysilicic acid or a small zeolite crystallite was described as a weighted undirected graph. In such an approach, the surface T atoms at the reaction site of hydrolysis was then described a convex hull. The hydrolysis was then described as the topology transformation of corresponding node connection in the undirected graph. Considering the potential large structural difference between the reactants and products of the hydrolysis, atomic structures of the products can then be derived by projection of the undirected graph back to atomic structure of the reactant and subsequent structural optimization. Energy and Gibbs free energy calculation and structure analysis routes were also implemented. This approach enables operando investigation of the structure and energy evolution of polysilicic acids at conditions of hydrothermal synthesis.