Comparative study of the properties of ionic solids from density functionals

Prediction of ionic-solid properties presents a great challenge to Kohn–Sham conventional density functional theory, due to the fact that there is strong van der Waals interaction between ion cores. In this work, we apply the Tao-Mo (TM) semilocal density functional to calculate lattice constants, bulk moduli, and cohesive energies for ionic solids consisting of alkali halides, silver halides, and other ionic solids. Our calculation shows that the TM functional yields accurate lattice constants, with a mean absolute error (MAE) of 0.087 Å, which is obviously smaller than commonly-used semilocal functionals such as the local spin-density approximation (LSDA) and Perdew–Burke–Ernzerhof generalized gradient approximation (PBE GGA). It is even more accurate than dispersion-corrected density functional PBE + D3 (MAE = 0.116 Å). This is unexpected success. For bulk moduli, TM functional can also yield very good accuracy, with an MAE of 3.02 GPA. Finally, we evaluate the cohesive energies of ionic solids. We find that this functional produces an MAE of 0.13 eV/atom, which is more accurate than the LSDA and PBE GGA, but less accurate than PBE + D3. We have also made a comparison of TM with other semilocal density functional theory (DFT) methods on several other ionic solids. It appears that TM also gives an overall improvement upon other popular semilocal DFT methods such as PBE for solids and Tao–Perdew–Staroverov–Scuseria. (paper)