Efficient ab initio quantum mechanical simulations of structural stability and vibrational properties of bulk, monolayer and (<i>n</i>,0) nanotubes: Yttrium sesquioxide Y₂O₃

Abstract

Abstract In this contribution, we report reliable ab initio quantum mechanical simulations of a variety of physical properties concerning yttrium sesquioxide (Y 2 O 3 ) in different arrangements from the bulk, the monolayer ( h ‐Y 2 O 3 ), to the ( n ,0) single‐walled nanotubes in the range from n = 6 to 32, for geometry optimization and vibrational properties. Structural parameters, phonon wavenumbers, infrared (IR) and Raman intensities, and elastic constants are computed via density functional theory (DFT/B3LYP) where the trend towards the ( h ‐Y 2 O 3 ) monolayer for large nanotube radius is discussed. We firstly report combined experimental and computational studies on the structural and vibrational properties of the bulk Y 2 O 3 . Then, IR and Raman spectra of all arrangements are simulated via the coupled perturbed Hartree–Fock and Kohn–Sham (CPHF/KS) computational schemes. For the ( n ,0) Y 2 O 3 nanotube family, two sets of IR active phonon modes in the (200–400 cm −1 ) and (600–900 cm −1 ) ranges are determined. Both of them tend smoothly with different slope, towards the optical vibrational modes of the h ‐Y 2 O 3 single layer. Three sets of active phonon bands are obtained in their Raman spectrum. The first one, in the 0–100 cm −1 range contains two phonon modes, their vibration wavenumbers tend to zero at very large tube radius and are found to be connected to the elastic constants C 11 and C 66 of the h ‐Y 2 O 3 monolayer as the 1D → 2D transition is approached. The second one, in 200–400 cm −1 range tends to the optical mode E ′ ( ν = 308 cm −1 ) of the monolayer. The third set, in the 600–900 cm −1 range contains two active modes, their intensities tend to zero in the limit of large nanotube without change in their vibration wavenumbers.