Abstract/Summary

The perovskite structure is common to a wide range of materials which exhibit a rich variety of physical properties, such as ferroelectricity, antiferromagnetism, piezoelectricity, giant magnetoresistance, etc. along with different types of phase transition (metal-insulator, magnetic, ferroelectric and structural transitions). The control of the physical properties of perovskites by varying temperature, pressure, composition, and external fields give rise to novel phases. With continued advances in computational power, algorithms and simulation techniques, computational research has become increasingly effective in understanding and complementing experiments. In particular, density functional theory (DFT) based simulations provide fundamental insights into structural stability and properties of a material under the influence of external stimuli. On the other hand, classical and quantum atomistic modelling of materials helps in the study of their properties at long length and time scales by using molecular dynamics. In this thesis, I use DFT and ab initio molecular dynamics (AIMD) to model functional perovskites. This thesis deals with various types of perovskites based on the kind of atomic/molecular species constituting the perovskite structure and explains the complex interplay between structure and properties in these materials. Starting with an inorganic multiferroic perovskite, BiFeO3, the effect of cobalt doping in BiFeO3 on its structural, electronic, ferroelectric and thermodynamic properties is explored, in the context of potential photocatalytic applications. I present an AIMD investigation of the structural, electronic, vibrational and thermodynamic properties of mixed-cation mixed-anion perovskite solid solution of FAPbI3 and MAPbBr3 for photovoltaic applications. Finally, I study molecular perovskites and the phase transitions observed in them, which can be employed for solid-state refrigeration applications based on the barocaloric effect. The effect of different metal cations on the mechanical properties is calculated, which provides a starting point for rational design of molecular perovskites with strong barocaloric behaviour. This work illustrates the rich diversity in behaviour of perovskite-based materials and how first principles simulations can make substantial contributions to understanding and controlling their functional properties.