Ab initio study for electronic and crystal structure of NiTi R-phase

We present ab initio calculations of the electronic and crystal structure for the R-phase of NiTi shape memory alloy. Our calculations have been performed using the density functional theory with plane-wave pseudopotentials. Based on two reported lattice symmetries, P3 and , for the R-phase, we carried out geometry optimization and compared the ground-state energies, total density of states (TDOS) and bond lengths between the two structures after geometry optimization. After geometry optimization, the P3 structure changes into a P31m structure, while the structure is unchanged. The P31m structure has lower energy and TDOS at the Fermi energy than that of the structure. Based on the low-energy P31m model, we suggest that the P31m structure is the correct crystalline ground state of the R-phase.