Papers by Keyword: van der Waals

Abstract: The crystal structure, electronic and optical properties of organic molecular crystal Trans-4-(trifluoromethyl) cinnamic acid (4-TFMCA, C₁₀H₇F₃O₂) were studied using the density functional theory (DFT). Since 4-TFMCA undergoes solid-state photodimerization under an external light source (UV), the optical properties were a subject of interest. In the calculations, experimental lattice parameters were obtained from previous studies and used as an initial geometry. Structural optimization was achieved using the vdW-DF2 functional with norm-conserving pseudopotentials (NCPP). To optimize the crystal structure, the Birch-Murnaghan equation of state (EOS) was used, and the total volume showed a decrease of 2%. The electronic band structure of the 4-TFMCA crystal was first calculated. The electronic and optical band gaps were predicted, and an artificial acceptor level, attributed to the unsaturated carbon and hydrogen atoms in the molecule, was observed. Additionally, optical properties such as the dielectric function, reflectivity, loss function, refractive index, and absorption coefficient were computed.

Abstract: Van der Waals (vdW) interaction is one of the important properties in the composite. The usual measurement used to investigate the vdW interaction between filler and polymeric binder is FTIR spectroscopy where the result obtained is the band shift appearance, however, it has not been used yet to estimate the vdW magnitude. Using the Lennard-Jones potential, we developed a new analysis method to obtain approximately its magnitude and further the distance between filler atoms and polymeric group. We used our model proposed to several data reported by some authors, and interestingly we also found an appearance of anharmonic vibration of the atoms.