Title: DFT Predicted Phase Transition for GdI2 Under Pressure

GdI2 has long been studied for its magnetic properties in bulk along with being layered in thin films. However, less is known about how the structure and properties change under pressure. Our first principles density functional theory (DFT) calculations predict the bulk ambient pressure 2H-MoS2 type structure of GdI2 with antiparallel, prismatic polyhedra enthalpically competes with a similar structure with differently aligned polyhedra for low hydrostatic pressure. At higher pressures, our calculations predict a structure with distorted polyhedra is favored over the ambient pressure phase beyond 4 GPa. This understanding can be used for the mechanochemical control of di- and trihalide materials.