7 - Amino Acid Anhydrous Crystals

Summary

Density functional theory computations within the local density approximation and generalized gradient approximation, in pure form and with dispersion correction, were carried out to investigate the structural, electronic, and optical properties of several amino acid anhydrous crystals. The electronic (band structure and density of states) and optical absorption properties were used to interpret the light absorption measurements performed at room temperature. Mulliken and Hirshfeld population analysis were also performed to assess the degree of charge polarization in the zwitterion state of some amino acid molecules in the DFT converged crystal. Different dielectric function profiles obtained for some of the most important symmetry directions also demonstrate the optical anisotropy of the amino acid anhydrous crystals. The infrared absorption and Raman scattering spectra were recorded and interpreted, with their normal modes assigned. The complex role of water on the carrier transport properties in the monohydrated aspartic acid crystals is also highlighted.