Optical absorption and electronic band structure first-principles calculations ofα-glycine crystals

First principles determination of structural, electronic and lattice dynamical properties of a model dipeptide molecular crystal

“…The valence bands displayed are extremely narrow, displaying little dispersion across the Brillouin zone, indicating that electronic orbitals are primarily localised on each molecule in the unit cell. Such localisation is consistent with hydrogen bonding being the dominant mechanism responsible for the crystal structure; similar findings have been reported concerning the electronic structure of amino acid molecular crystals [55,71]. Inspection of the eigenvalues reveals that for the highest occupied valence bands the Davydov splitting (i.e.…”

“…Nitrogen and carbon atoms each provide a contribution that is between approximately one sixth and one fifth that of the oxygen atoms to the HOMO states, with the nitrogen providing slightly more states. Decomposing the nitrogen local density of states into both amine and amide nitrogen contributions (not shown), it is found that the amine nitrogen makes a negligible contribution to the bandstructure in the vicinity of the bandgap, consistent with recent work concerning the electronic structure of the glycine molecular crystal [71]. In contrast to the amine nitrogen atom, the amide nitrogen atom is found to provide a more substantial contribution to the electronic states near the bandgap (not shown).…”

“…In comparison, the direct bandgap corresponding to Γ − Γ transitions is 5.00 eV. As DFT calculations often obtain underestimates of the bandgap [71], this suggests that the glycyl-l-alanine crystal possesses an insulating character. These values are in close agreement with existing theoretical estimates of the bandgap for both crystalline alanine [55] and glycine [71].…”

“…As DFT calculations often obtain underestimates of the bandgap [71], this suggests that the glycyl-l-alanine crystal possesses an insulating character. These values are in close agreement with existing theoretical estimates of the bandgap for both crystalline alanine [55] and glycine [71]. In the absence of experimental data with which to compare directly, we note that experimental optical absorption measurements indicate a bandgap of 5.11 eV for crystalline α-glycine; it is perhaps possible to anticipate that the experimental value for glycyl-l-alanine is similar.…”

Surface enhanced Raman spectroscopy and quantum chemical studies on glycine single crystal

“…6 shows the HOMO and LUMO of Gly and Gly-Ag. The band gap energy value of Gly is found to be 5.12 eV, which agrees well with the previously reported value [36]. It is also interesting to note that, the reduced band gap energy value (1.06 eV) is obtained when Gly adsorption on silver surface, which can be correlated to the transfer of electron density associated with the process of adsorption [20].…”