L-asparagine crystals with wide gap semiconductor features: Optical absorption measurements and density functional theory computations

Abstract

Results of optical absorption measurements are presented together with calculated structural, electronic, and optical properties for the anhydrous monoclinic L-asparagine crystal. Density functional theory (DFT) within the generalized gradient approximation (GGA) including dispersion effects (TS, Grimme) was employed to perform the calculations. The optical absorption measurements revealed that the anhydrous monoclinic L-asparagine crystal is a wide band gap material with 4.95 eV main gap energy. DFT-GGA+TS simulations, on the other hand, produced structural parameters in very good agreement with X-ray data. The lattice parameter differences Δa, Δb, Δc between theory and experiment were as small as 0.020, 0.051, and 0.022 Å, respectively. The calculated band gap energy is smaller than the experimental data by about 15%, with a 4.23 eV indirect band gap corresponding to Z → Γ and Z → β transitions. Three other indirect band gaps of 4.30 eV, 4.32 eV, and 4.36 eV are assigned to α3 → Γ, α1 → Γ, and α2 → Γ transitions, respectively. Δ-sol computations, on the other hand, predict a main band gap of 5.00 eV, just 50 meV above the experimental value. Electronic wavefunctions mainly originating from O 2p-carboxyl, C 2p-side chain, and C 2p-carboxyl orbitals contribute most significantly to the highest valence and lowest conduction energy bands, respectively. By varying the lattice parameters from their converged equilibrium values, we show that the unit cell is less stiff along the b direction than for the a and c directions. Effective mass calculations suggest that hole transport behavior is more anisotropic than electron transport, but the mass values allow for some charge mobility except along a direction perpendicular to the molecular layers of L-asparagine which form the crystal, so anhydrous monoclinic L-asparagine crystals could behave as wide gap semiconductors. Finally, the calculations point to a high degree of optical anisotropy for the absorption and complex dielectric function, with more structured curves for incident light polarized along the 100 and 101 directions.

Quantum confined peptide assemblies with tunable visible to near-infrared spectral range

“…1f ). Specifically, the band gaps (Δ E ) of cyclo-FW and cyclo-WW were calculated to be 3.63 eV and 3.56 eV, respectively, indicating their wide-gap semiconductive nature 36 , 37 . This implies that the dimerization was mostly driven by π – π interactions between aromatic side-chains, especially the indole rings.…”

Exploring the mechanism of isomerisation and water-migration in the water-complexes of amino-acid l-proline: electrostatic potential and vibrational analysis

“…2 and natural population analysis (NPA), 51 though an iterative version 52 of the Hirshfeld scheme has recently been found to be more useful, for example, in a study on L-asparagine. 53 For the zwitterionic complexes Z1 and Z2 as well as for the conformers P1 and P4 of L-proline and their most relevant water-complexes, Table 3 compares the partial atomic charges computing using the CM5, HPA, MPA, NPA methods at the BHandHLYP/6-311++G(d,p) level of the theory. It is evident that in the zwitterionic complexes Z1 and Z2, the charge on the nitrogen atom N(1) of NH 3 group is positive (less negative) than that on the oxygen atom O(1) of carboxylic group in L-proline, thereby, revealing a dipolar nature of the explored zwitterionic complexes of L-proline with a single-water molecule.…”

Computational structural, electronic and optical properties of the palmitic acid in its C form

“…5, shows the effective mass calculated of the holes and electrons through the fitting quadratic curves (red dots) at points of interest around the Brillouin zone. Here, we aim to estimate the electronic transport behavior along the directions of the crystal from the maximum point of the valence band (holes) and minimal point of the conduction band (electrons) [37][38][39]. Effective mass * furnishes the assess the mobility of charge carriers at a given point along theˆ direction, according to the equation…”