Density Functional Dependence in the Theoretical Analysis of the Terahertz Spectrum of the Illicit Drug MDMA (Ecstasy)

In this paper, the experimental terahertz (THz) spectrum of the illicit drug 3, 4-methylenedioxymethamphetamine hydrochloride (MDMA.HCl, C₁₁H₁₆O₂N⁺·Cl^-) has been rigorously modeled using solid-state density functional theory (DFT). The compound MDMA.HCl is more widely known by the street name ¿Ecstasy¿ and is a commonly abused drug. The first-principles simulation and assignment of the experimental THz absorption features is a key step in the validation of the spectrum for use in spectral databases for illicit compound sensing. This theoretical study includes the use of an array of generalized gradient approximation density functionals in order to provide a thorough understanding of the performance of the various functionals in the simulation of this crystalline drug. Of the seven studied functionals, the BP functional yielded superior agreement with the experimental data in terms of intramolecular structure, and in the position and intensity of spectral features.