Abstract
The electronic band structure of both the monoclinic and orthorhombic
cysteine polymorphs is investigated using density functional theory
(DFT) calculations in the generalized gradient approximation (GGA).
Besides, orthorhombic cysteine crystals were grown, and their optical absorption was measured, being estimated an energy gap of E-g(exp) =
4.68 eV for recrystallized cysteine powder. The existence of a small
secondary optical absorption structure for the recrystallized sample
around 4.4 eV suggests the existence of defect levels inside the band
gap. The calculated valence and conduction bands are very flat for both
cysteine polymorphs, suggesting that they are insulators. (C) 2011
Elsevier B.V. All rights reserved.
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