Efeitos térmicos em parâmetros de intensidade de compostos com íons lantanídeos: Um estudo computacional

Abstract

Lanthanides are elements that have the oxidation of stable trivalent ions, where their electronic structure has an incomplete 4f layer, providing a shielding effect for the electrons of that layer. The 4f-4f transitions are important for the mechanisms involving the Judd-Ofelt theory and the calculation methods involving thermal effects and the intensity parameters developed in this work. The Judd-Ofelt theory includes the forced electric dipole (FED) and dynamic coupling (DC) mechanisms to account for electronic transitions in lanthanide compounds. The JOYSpectra program developed by our research group uses this theory to calculate the intensity parameters Ωλ, (λ = 2, 4 e 6), including the SOM (Simple overlap model) and BOM (bond overlap model) overlap models for treating the covalence effects of the bonds between the lanthanide and the binders. In this work, the objective is to implement in the JOYSpectra code developed in C language two new algorithms, called Variational Cube and Distorted Normal Modes. The variational cube model includes thermal effects on the Ωλ, with several displacements related to the volume of a cube in the positions of the binders as a function of temperature. It was implemented, without JOYSpectra, the functionality that promotes simulation of a large number of spatial configurations (N≈106), in which the displacement limits of each atom are given through the Bose-Einstein population, which relates the temperature and the length of the box (L). The new implementation was tested in the EuCl6 system, for which values of intensity parameters Ω2 are found at temperatures 77 K and 300 K, obtained by Carneiro Neto, 2019 for comparison with the results of the Variational Cube algorithm. The results indicate that, as expected, close to 100 K the behavior of the Bose-Einstein population is similar to that of a Boltzmann population. The Distorted Normal Modes algorithm operates small variations in the displacement vectors that are attributed to each normal mode of the coordinated species. Such variations, which simulate the thermal effects, are used in this model to evaluate the intensity parameters Ωλ. The difference between the models is related to the variables involved, where the population weight for each geometric displacement is counted in the model in the normal modes.