Coarse grained models for large scale atomistic simulations of spin and lattice dynamics

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Coupling effects in magnetocaloric materials systems will be investigated by density functional theory (DFT), tight binding and bond order potential methods. Through a cooperative effort with our partners in this package proposal we want to achieve an in-depth understanding of the magnetostructural phase transitions in magnetocaloric materials and based on this contribute to an optimization of this materials class. Within this project, we will develop atomistic bond order potentials with sufficient accuracy for the simulation of magnetocaloric materials. This goal will be achieved through a systematic coarse graining of the electronic structure starting from an accurate density functional representation. The bond order potential will allow for O(N) molecular dynamics simulations and will add an additional length and time scale compared to DFT. This will allow for the simulation of microstructure elements like the dynamics of twin and grain boundaries as well as for a direct evaluation of energetic/entropic contributions in connection with the magneto-structural phase transition. Furthermore, In a close collaboration with our experimental partners we will perform accurate all electron calculations in order to optimize known and investigate possible new magnetocaloric materials. The influence of alloy composition, strain and magnetic field will be studied for Y-Co Ce-Fe based systems.