First-principles analysis on phase transition, atomic, electronic, and mechanical properties of kaolinite under pressures

Kaolinite is the major clay mineral and dispersed widely in topsoil and subsoil in the world. The structural, electronic, and mechanical properties of kaolinite are closely related to their various applications in architecture, industry, and agriculture. In the present paper, the phase transition, atomic structural, electronic and mechanical properties of kaolinite under pressure range of 0-10 GPa were systematically investigated using the firstprinciples density functional theory (DFT). The lattice parameters, bonding nature, total and partial density of states, elastic constants, various modulus, and anisotropy for kaolinite were calculated. The transition pressures of kaolinite occurred at 4.93 GPa (kaolinite-I -> kaolinite-II) and 8.23 GPa (kaolinite-II -> kaolinite-III), respectively, which were well consistent with experimental data. In the range of 0-10 GPa, the lattice parameters, volume, and typical bond lengths of I, II, and III phases of kaolinite were decreased with increasing pressure. Meanwhile, the calculated density of states, charge density distribution, and band structures had little change with increasing pressure, implied that effects of pressure on electronic property of three phases of kaolinite were weak and corresponding structures were stable. Finally, the elastic constants results of I, II, and III phases of kaolinite implied that (001) plane anti-deformation ability was weaker than (100) and (010) planes and shear deformation resistance of (001) was stronger than these of (100) and (010) plane. The results of bulk modulus, shear modulus, and Young's modulus of the three phases of kaolinite indicated that the ability of kaolinite to resist volume deformation and shear failure was enhanced. Various mechanical quantities were evaluated and implied that the kaolinite-I and kaolinite-II was ductile, while the kaolinite-III in the brittle manner. The present theoretical calculations results are helpful to understand the physico-chemical and mechanical properties of natural kaolinite from the microscopic point of view and provided an important theoretical basis for the application of kaolinite in fields of architecture, industry, and agriculture.