Theoretical Investigation on the Terahertz Vibrational Spectroscopy of Amino acid Crystal

The terahertz (THz) theoretical spectra of solid-state amino acids were investigated in this paper. Based on the dispersion-corrected density functionals, the periodic crystal structures were constructed. It is found that B3LYP-D2 can produce more accurate simulation results, however, it also greatly increases the cost of calculations. The combination of PBE with the 6-311G(d,p) basis set is accurate enough to reproduce the experimental THz spectra of solid-state amino acids with much higher simulation speed. The observed spectral features were assigned as primarily external lattice translations and rotations with lesser contributions due to intramolecular torsions.