The martensitic transition temperature (MTT) of a shape-memory alloy (SMA) is one of its most important characteristics, determining its operating temperature, while the energy difference ($\mathrm{\Delta }E$) between the austenite and martensite phases is among the most crucial factors dictating MTT. Using density-functional theory, $\mathrm{\Delta }E$ of NiTi, the most studied and commonly used SMA, varies from 23 to 116 meV/atom, depending on the density functional [Wu and Lawson, J. Chem. Phys. 161, 134104 (2024)]. Consequently, free-energy calculations using different density functionals yield MTTs that differ by several hundred K. Here, we benchmark $\mathrm{\Delta }E$ of NiTi using diffusion quantum Monte Carlo. With this method, the energy difference is estimated to be $70.9\pm 2.5$ meV/atom.

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• Metals
• Shape-memory materials
• Density functional theory
• Diffusion quantum Monte Carlo