Hydrogen Bond in Layered Materials: Structural and Vibrational Properties of Kaolinite by a Periodic B3LYP Approach

Extensive modeling of structural and vibrational properties of OH groups in kaolinite, a representative member of the clay family, has been studied within a periodic approach using the CRYSTAL03 program and adopting B3LYP functional with a polarized double-ζ Gaussian basis set. Optimized geometry and corresponding frequencies inclusive of the anharmonicity of all possible OH groups of kaolinite (inner, inner surface, and outer surface) are in overall good agreement with the structural and vibrational experimental data. Calculations definitely show that all inner surface OH groups are involved in weak interlayer hydrogen bonds, resulting in a B3LYP interlayer cohesive energy of about 32 kJ/mol per unit cell computed with a basis set of polarized triple-ζ quality. While the maximum error of the B3LYP OH stretching frequencies compared to experiment is around 20 cm - 1, exploration of the potential energy surface of the OH groups reveals that the large amplitude motion of some of them is possible at room temperature, which accounts for the presence of some broadness and extra bands in the infrared experimental OH stretching region. Calculations on a single kaolinite slab extracted from the bulk structure gives clear insight on the electrostatic complementary which holds the structure in place and allows the role of the OH groups at the external surface of layered materials to be understood.