Modelling of the electronic and ferroelectric properties of trichloroacetamide using Monte Carlo and first-principles calculations

The electronic structure and ferroelectric mechanism of trichloroacetamide were studied using first principles calculations and density functional theory within the generalized gradient approximation. Using both Bader charge and electron deformation density, large molecular spontaneous polarization is found to originate from the charge transfer cause by the strong “push-pull” effect of electron-releasing interacting with electron-withdrawing groups. The intermolecular hydrogen bonds, N H⋯O, produce dipole moments in adjacent molecules to be aligned with each other. They also reduce the potential energy of the molecular chain threaded by hydrogen bonds. Due to the symmetric crystalline properties, however, the polarization of trichloroacetamide is mostly compensated and therefore small. Using the Berry Phase method, the spontaneous polarization of trichloroacetamide was simulated, and good agreement with the experimental values was found. Considering the polarization characteristics of trichloroacetamide, we constructed a one-dimensional ferroelectric Hamiltonian model to calculate the ferroelectric properties of TCAA. Using the Hamiltonian model, the thermal properties and ferroelectricity of trichloroacetamide were studied using the Monte Carlo method, and the Tc value was calculated.