Improving the density functional theory prediction accuracy for elastic moduli and thermal expansion of MoAlB, Fe₂AlB₂, and Mn₂AlB₂

The elastic moduli and thermal expansion of MoAlB, Fe2AlB2, and Mn2AlB2 are investigated by first-principles calculations, in particular to improve the density functional theory (DFT) prediction accuracy after clarifying the critical role of their lattice constants. By calculating the lattice constants and elastic moduli using the typical exchange-correlation functionals, the observed positive correlation between the calculation errors of elastic moduli and those of cell volumes suggests a method to significantly improve the calculation accuracy for elastic moduli using the experimental cell volume to correct the input model (volume correction method), resulting in satisfactory results. Furthermore, a two-step strategy is proposed for the precise high-temperature elastic moduli with the help of quasi-harmonic approximation for the most accurate high-temperature cell volume using an exchange-correlation functional in the first step, and another one used in the volume correction method in the second step. Similarly, the calculation accuracy of thermal expansion also heavily depends on that of cell volumes and configurations, where their thermal expansion is estimated with great accuracy by using the exchange-correlation functional that well reproduces the lattice constants.