The Research Of Potential Function And Molecular Dynamics Simulation Of SrTiO₃

As an important perovskite type material with excellent dielectric and photoelectric properties, SrTiO₃ (STO) is widely used in various fields. The films of it were used in high frequency microwave devices, and have greatly potential application in non-volatile random access memory.Molecular dynamics (MD) simulation, as an important method, was widely applied in various materials research. The most advantage of MD is that the atomic structure characters and properties can be obtained by this kind of simulation. The potential function is a key factor in MD simulation. For simple structure material, such as metal, there exists a most applicable potential function, EAM, which greatly promote the simulation research of this kind of material. On the contrary, we haven't suitable potential function for complex material system such as perovskite type material, which limit the simulation research in this kind of material system. In this dissertation, the first principle will be adopted to calculate the electronic structures and simulate the interaction of STO, based on which, the potential function of it will be built.In this dissertation, the crystal and amorphous model of STO and BTO was built for first principle simulation, and the electronic structure of these system were calculated. Through discussion of the density of states, density of charge and Mulliken population analysis, the conclusion was drawn: In STO and BTO, the interaction of Ti and O consists of both ionic and covalent character, although the later one is lower in amorphous state. The interactions in other atom pairs are mainly ionic. Because of the covalent interaction, the ionic charge is not the same as the typical chemical state. From the interaction characters of these material systems, the potential function, named as Partial Ionic Model (PIM) was built, which consists of Coulomb, Born-Mayer and Morse potential, representing Coulomb interaction, ionic interaction and covalent interaction respectively. The parameters of this potential function were fitted by the energy face of the material system calculated from first principle simulation.In order to verify the potential function, the MD simulations of crystal structure and melting procedure of STO were carried on, which draws out that, the MD simulation successfully reproduced the crystal structure of STO in room temperature, and the simulating melt point , 2430K, is agree well with the laboratory value, just 2.1% higher. The simulations resulted in that the potential function built by first principle simulation can properly represent the atom interaction in STO.At last, the structure and dynamical characters of amorphous and crystal STO were simulated by MD, which concluded that in amorphous the orderly arrangement of atom only exist in most neighbor layer, and the coordination chemistry of Ti is about 38% in 5 folks, agree well with experiment value.