Abstract
Density functional calculations were performed to study the properties
of the three main glycine solid-state polymorphs alpha, beta, and gamma
and the glycine dehydrate (GDH) crystal. Optimized unit cell geometries,
Kohn-Sham electron energy bands, electron densities of states,
population charges, carrier effective masses, optical absorption, and
complex dielectric functions were obtained for each glycine system using
a GGA functional plus the TS dispersion correction, leading to lattice
parameters very close to the experimental values. The theoretical
fundamental gaps of all glycine crystals are indirect and near 5 eV. The
carrier effective masses are anisotropic and especially heavy (similar
to 26 free electron masses at most) for holes in the case of the GDH
crystal. The optical absorption and the dielectric function are very
sensitive to the polarization of light in all glycine-based crystals.
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