Exploring structural, optoelectronic, and thermo-phononic properties of AcClO using DFT and AIMD

In this study, we present a comprehensive first-principles investigation into the structural, thermal, phononic, electronic, and optical properties of Actinium Oxychloride (AcClO). AcClO is a Matlockite-structured material containing a 5f radioactive element (Ac). Using four computational codes — CASTEP for density functional theory (DFT), Quantum Espresso for ab initio molecular dynamics (AIMD), Phonopy for phonon and heat capacity, and Phono3py for thermal conductivity and group velocity — we confirmed the energetic, dynamic, mechanical, and thermal stability of AcClO, through calculations of the formation energy, phonon dispersion, elastic constants, and AIMD simulations, respectively. Furthermore, bonding analysis through electron localization function (ELF) shows that AcClO is an ionic compound. Band structure (including the hybrid HSE06 functional), partial density of states (PDOS), and spin-polarized total DOS show that AcClO is a wide band gap and non-magnetic semiconductor. The heat capacity, entropy, and phonon PDOS analyses provide insights into the vibrational dynamics of AcClO, revealing interplay of atomic vibrations between the heavy Ac atoms and lighter O atoms. In computations of the complex dielectric function, refractive index and optical conductivity, we find that AcClO exhibits a high static dielectric constant and collective plasmons in the far ultraviolet spectrum. Bearing in mind the radioactive nature of AcClO, along with its predicted low lattice thermal conductivity, wide band gap, and high dielectric constant, it could be used for applications such as deep-sea thermal insulation devices and space UV-sensor housings. This first theoretical exploration of AcClO marks a significant contribution to the understanding of Matlockite-type structures and actinide-based oxychlorides.