Faculty of Physics - University of Bucharest

UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

Guest
2026-06-11 23:58

HOME CONFERENCES SEARCH LOGIN NEW USER IMAGES

Conference: Bucharest University Faculty of Physics 2026 Meeting

Section: Solid State Physics and Materials Science

Title:

Ab Initio and Molecular Dynamics Studies of Amorphous TiO2/SiO2 Mixed Oxide Phases for Optical Coatings

Authors:

Mihaela COSINSCHI (1,2,3), Amanda T. PREDA (1,2), Nicolae FILIPOIU (1, 2, 3), Calin A. PANTIS-SIMUT (1, 2), Diana MANEA (1,2), Alaa ALLOSH (1,2), George A. NEMNES (1,2,4)

^*
Affiliation:

(1) Horia Hulubei National Institute for Physics and Nuclear Engineering, Magurele-Ilfov 077126, Romania

(2) University of Bucharest, Faculty of Physics (Doctoral School of Physics), Magurele-Ilfov 077125, Romania

(3) National Institute of Materials Physics, Magurele, Ilfov 077125, Romania

(4) Research Institute of the University of Bucharest (ICUB), 90 Panduri Street, Bucharest 050663, Romania

E-mail

rada.cosinschi@s.unibuc.ro

Keywords:

molecular dynamics, material modeling, density functional theory, ab initio calculations, amorphous oxides

Abstract:

High-reflectivity mirror coatings for laser applications often rely on rugate filters, optical devices designed to continuously adjust the refractive index of the medium, reducing interface scattering between adjacent dielectric layers and improving transmission throughout the device [1]. Alternating titanium dioxide (TiO2) and silicon dioxide (SiO2) layers are often used in coatings to exhibit this effect in practice, although the abrupt interface between them introduces optical and structural discontinuities that affect performance [2]. To address this issue, a diminishing effect may be achieved including a mixed oxide (TixSi1-xO2) as a physically motivated interfacial placeholder, smoothing transitions between the two materials. We present a computational workflow for generating amorphous TiO2, SiO2 and mixed TixSi1-xO2 structures using a combination of classical molecular dynamics simulations and density functional theory (DFT). Firstly, amorphous cells are produced starting from arbitrary configurations by employing a simulated annealing (melt and quench) protocol implemented in LAMMPS [3], using established interatomic potentials [4] for each individual oxide. The resulting configurations are then relaxed and characterized using density functional theory (DFT) calculations performed with SIESTA code[5], extracting the structural and electronic properties of the final super-cells and comparing them against available theoretical values for the amorphous materials. Mixed-phase structures are subsequently constructed from the validated amorphous cells by substituting a controlled fraction x = 0.04-0.5 of cation sites (Ti or Si), followed by a structural relaxation to account for the differing coordination preferences of the two species. Several distinct structures have been considered, both for the starting amorphous materials, as well as for swapped atoms, in order to create a statistical overview. This methodology provides a tractable and reproducible route to the desired structures, laying the groundwork for further refined modeling, electronic and optical properties calculations, and ultimately their integration into rugate coating simulations.

References:

[1] Jupe et al., Proc. SPIE 6403, Laser-Induced Damage in Optical Materials: 2006, 640311

[2] Bercea et al., Rom. J. Phys. 63, 606 (2018)

[3] https://www.lammps.org

[4] https://openkim.org/

[5] https://siesta-project.org/siesta/

Acknowledgement:

This work was supported by the Romanian Ministry of Research and Innovation under the project ELI-RO-OMP 3/2025.