Determination of the Cohesive Properties and Sublimation Temperatures of Glycine Polymorphs

Abstract

The experimental data of sublimation properties is limited to important materials, encouraging the development and assessment of theoretical models. Here, such properties were evaluated from periodic density functional theory calculations for three glycine polymorphs (α, β, and γ-glycine) along with the quasi-harmonic approximation for the determination of thermodynamic properties. Careful treatment of cohesive properties was performed, which are shown to be fundamental in the glycine dynamic sublimation process due to its zwitterionic nature in the crystalline environment in contrast with the molecular form in the gas phase. Computational limitations are addressed, and a detailed treatment of vibrational modes of crystalline and vapor phases is discussed. Also, the agreement with the fundamental physical-chemical background on the glycine sublimation process, obtained from different computational methodologies, is discussed. The uncertainties of sublimation properties were evaluated. The maximum absolute deviation of the sublimation temperature, from the experimental data for α-glycine, within the pressure range from 0.1 to 1 Pa, was -5.31 K. Our findings corroborate the experimental evidence for the preferential recrystallization of gas-phase glycine into the metastable β phase.