http://202.45.146.37:8080/jspui/handle/123456789/445 PHD Thu, 27 Aug 2026 00:34:57 GMT 2026-08-27T00:34:57Z http://202.45.146.37:8080/jspui/handle/123456789/447 Title: FIRST-PRINCIPLES STUDY OF MECHANICAL, ELECTRONIC, MAGNETIC AND OPTICAL PROPERTIES OF SELECTED SINGLE AND DOUBLE PEROVSKITES Authors: POKHAREL, PESHAL Abstract: Perovskites are crystalline materials represented by the general formula ABX3. Their simple crystal structure leads to a broad range of electrical, catalytic, optical, magnetic, piezoelectric, dielectric, and magnetoresistive properties. Due to their remarkable properties, perovskites have been widely utilized in thin-film capacitors, optoelectronic devices, non-volatile memory, solar cells, data storage technologies, spintronic devices, lasers, sensors, high-temperature coatings, and frequency filters. In the present work, we investigate the mechanical, electronic, magnetic, and optical properties of zirco- nium silicate (ZrSiO3) perovskite (under different hydrostatic pressures, surface termi- nations, different layer configurations, and its monolayer form); europium (Eu)– and yttrium (Y)–doped samarium manganite (SmMnO3); and the double perovskite stron- tium zirconium molybdate (Sr2ZrMoO6) using first-principles density functional theory (DFT) calculations. For bulk calculations, the Perdew–Burke–Ernzerhof (PBE–GGA) exchange–correlation functional was used, whereas the Perdew–Burke–Ernzerhof for solids (PBEsol) functional was employed for surface and layered structures. Ultrasoft Vanderbilt pseudopotentials (USPPs) were adopted with plane-wave cutoff of 70 Ry for the wavefunctions and 560 Ry for the charge density. Brillouin zone sampling was performed using Monkhorst–Pack grids of 14 × 14 × 14 for bulk property calculations and 14 × 14 × 1 for the monolayer. Convergence thresholds were set to 10−6 eV for the total energy and 10−3 eV/Å for the atomic forces. The elastic constants were calculated using the stress–strain method. The present study shows that the bulk ZrSiO3 is an indirect band gap semiconductor. Its band gap value increases with rise in pressure and decreases with the increasing number of layers. The termination model has a smaller band gap (2.585 eV for ZrO– and 1.639 eV for SiO2– termination model) than the bulk model. Electronic band gap of ZrSiO3 monolayer increases under compressive strain and decreases under tensile strain. Pristine SmMnO3 shows ferromagnetic half–metallic behaviour, and has the band gap of 2.72 eV. Its value substantially reduces with the in- troduction of Eu and Y dopants. The Sr2ZrMoO6 double perovskite exhibits an indirect band gap semiconductor with ferromagnetic behaviour. Elastic property calculations confirmed the mechanical stability and ductility of bulk ZrSiO3 up to 100 GPa. Both ZrO– and SiO2–terminated models of ZrSiO3 are also mechanically stable and ductile. The ZrSiO3 monolayer exhibits mechanical stability and ductility from -6% to +6% strain values. The pristine and Eu– and Y– doped SmMnO3, the material preserves its mechanical stability and ductility, even at a 25% substitution level. The stiffness of pristine SmMnO3 decreases with Eu– doping and increases with Y– doping. Elastic calculations of double perovskite Sr2ZrMoO6 under isotropic pressures from 0 to 80 GPa reveal significant elastic anisotropy, with distinct pressure–dependent behaviors. ix Magnetic analysis reveals that the magnetic moment of SmMnO3 increases with Eu– doping, whereas Y– doping leads to a reduction. Curie temperature of pristine SmMnO3 raises with Eu– doping, whereas lowers with Y– doping. The real and imaginary parts of dielectric function of ZrSiO3 increase with pressure, with absorption edges and sharp peaks shift to higher energies as pressure increases from 0 to 100 GPa. The refractive index and reflectivity of SmMnO3 decreases with Eu– and Y– dopings. The tunable electronic and optical properties of ZrSiO3 under pressure, mechanical strain, surface termination and 2D form indicated the material is suitable for flexible electronic devices and nano–electronics. The enhanced magnetic and electronic properties of Eu–and Y– doping on SmMnO3 indicate its application in magnetic sensors and data storage devices. Description: FOR THE AWARD OF DOCTOR OF PHILOSOPHY IN PHYSICS Wed, 01 Jul 2026 00:00:00 GMT http://202.45.146.37:8080/jspui/handle/123456789/447 2026-07-01T00:00:00Z