DFT calculations of the structural, electronic, optical and vibrational properties of anhydrous orthorhombic L-threonine crystals

Abstract

The structural, electronic, optical, vibrational and thermodynamic properties of the anhydrous orthorhombic L-threonine crystals are investigated by ab initio simulation using a pseudopotential approach within the density functional theory (DFT) method. We have considered both the generalized gradient approximation with dispersion correction (GGA + TS) and the local density approximation (LDA), respectively, as our exchange functionals. Within the GGA + TS calculations, an excellent agreement between the measured X-ray and our theoretical unit cell parameters was obtained, with deviations Δa,Δb,Δc of -0.08 Å, 0.12 Å, and 0.01 Å, respectively, for an 830 eV cutoff energy. Besides, a direct-band gap E(Γ→Γ) = 5.06 eV, was found in agreement with the experimental 4.96 eV result. The optical properties have been calculated considering [0 0 1] as the incidence direction of polarization of the incident light. The normal vibration’s modes, the infrared and Raman spectra of L-threonine, as well as the thermodynamic properties were also obtained and analyzed.