Electronic structure of complex oxides and sulphides, and statistical mechanics of N´eel and structural transitions from first-principles

Abstract

Oxides are mostly non-toxic and quite abundant in nature. They form an important class of materials due to their chemical and structural (halite, wurzite, spinel, corrundum, rutile, perovskite and pyrochlore) diversity. Oxides with transition metal ions have been studied greatly as these exhibit rich varieties of physical properties such as metallicity, semiconductivity, insulating, ferromagnetism, antiferromagnetism, ferroelectricity, antiferroelectricity, piezoelectricity, colossal magnetoresistance, superconductivity, charge and orbital orderings [1{9] along with a remarkable diversity in the nature of phase transitions (high-spin/low spin, metal-insulator, magnetic, ferroelectric and structural transitions) they undergo [2, 4, 5, 10{13]. The macroscopic properties of a material are a consequence of how electrons and atoms are arranged and held together in a solid. Since the motion of electrons (atoms) is governed by quantum mechanical laws (Newtonian mechanics), most of the physical properties can be determined in principle from these laws. Accurate evaluation of the macroscopic properties of a material directly from the fundamental equations ( rst-principles) of electrons is of fundamental importance, but also quite di cult.