Repository of University of Nova Gorica

Show document
A+ | A- | SLO | ENG

Title:Vibrational spectra of am-Al 2 O 3 : tuning a parametric model. : Written report: in fulfillment of Diploma Seminar 1FAF29 requirements
Authors:Jasmin, Kurtović (Author)
Luigi, Giacomazzi (Mentor) More about this mentor... New window
Files:This document has no files. This document may have a phisical copy in the library of the organization, check the status via COBISS. Link is opened in a new window
Language:Slovenian
Work type:Research project (high school) (p5)
Organization:FN - School of Science
Abstract:The present diploma seminar work has been dedicated first to the implementation of a procedure to calculate the vibrational density of states of two structural models of vitreous SiO 2 (v- SiO 2 ) and amorphous Al 2 O 3 (am-Al 2 O 3 ) models, and next to tune a parametric model for the calculation of the infrared (IR) spectra of am-Al 2 O 3 , in particular of the imaginary part of the dielectric function. The ground state of both structural models is obtained by relaxing the atomic structure by using the conjugate gradient method as implemented in the LAMMPS code. Vibrational frequencies and modes are obtained, in the harmonic approximation, by diagonalizing the dynamical matrices calculated for the given v-SiO 2 and am-Al 2 O 3 structural models. Dynamical matrices are obtained through a finite differences approach and vibrational density of states are plotted by applying Gaussian broadening. The calculation of the dielectric function requires the knowledge of the vibrational frequencies as well as the knowledge of the dynamical (or Born) charge tensors related to the atoms of the am-Al 2 O 3 structural model. For the latter model, a parametrization of the ab-initio Born charge tensors has been carried out with the purpose to allow for the fast calculation of the IR spectrum of any other am- Al 2 O 3 model without the need to calculate for it the Born charge tensors using expensive ab- initio methods. The parametrization of Born charge tensors takes into account, for aluminium atoms, only of the isotropic charge which depends on coordination number and average Al- O bond length of aluminium atoms, while for oxygen atoms coordinated to three Al atoms (75%), dynamical charges are parametrized also by the area bounded by aluminium atoms nearest neighbours of the 3-coordinated oxygen atom. Moreover for analyzing the dynamical charge tensors of 3-coordinated oxygen atoms a decomposition in terms of the representations of the spatial rotations was used. The IR spectrum obtained by means of the above described parametrization provides a good approximation to the IR spectrum obtained by using the ab- initio calculated dynamical charges, as it differs from it, on average, by around 5.1% which is much better (12%) than using a average isotropic charge model (i.e. diagonal Born charge tensors where each diagonal element is one third of the average isotropic charge).
Keywords:Vibrational spectra, am-Al 2 O 3, parametric model
Year of publishing:2021
Number of pages:36 str
COBISS_ID:76519427 Link is opened in a new window
URN:URN:SI:UNG:REP:YGKTMCYZ
Views:259
Downloads:0
Metadata:XML RDF-CHPDL DC-XML DC-RDF
Categories:Document is not linked to any category.
:
  
Average score:(0 votes)
Your score:Voting is allowed only for logged in users.

Hover the mouse pointer over a document title to show the abstract or click on the title to get all document metadata.

Back