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What Rules the Relative Stability of α‑, β‑, and γ‑Glycine Polymorphs?
journal contribution
posted on 2020-05-23, 03:43 authored by Neubi
Francisco Xavier, Antônio
Marques da Silva, Glauco F. BauerfeldtTheoretical
calculations based on the density functional theory,
using the PBE functional with the D3 dispersion correction under periodic
boundary conditions, have been employed aiming to investigate the
properties of α-, β-, and γ-glycine. Structural
parameters have been predicted with a maximum error of 1.42% for lattice
parameters and 2.53% for the unit-cell volume, for the α phase.
Band structure calculations suggest the band gap values of 4.80, 5.01,
and 5.23 eV for the α, β, and γ phases, respectively.
Quasi-harmonic calculations have been performed and the Gibbs free
energy function has been calculated in a wide range of temperature
and pressures, suggesting the stability ordering γ > α
> β, at room temperature, and the γ to α-glycine
phase transition temperature of 442.55 K, at 1 bar, in agreement with
the experimental findings. Moreover, a deviation from the experimental
value of only 0.44 J mol–1 K–1 is observed for the predicted S(α→γ) at 298.15 K. Finally, calculated sublimation enthalpies of 140.58,
138.09, and 141.70 kJ mol–1 (α, β, and
γ-glycine, respectively), at 298.15 K and 1 bar, have also shown
good agreement with the experimental values.