Effect of exchange-correlation functionals on the density functional theory simulation of phase transformation of fast-ion conductors: A case study in the Li garnet oxide Li7La3Zr2O12

The phase transformation of a fast-ion conductor Li7La3Zr2O12 (LLZ) upon heating was investigated using first-principle molecular dynamics by applying the local density approximation (LDA) and thirteen generalized gradient approximations (GGA) of the electron exchange and correlation (XC) energy functionals within the density-functional theory (DFT) framework. It was found that some functionals in the selected group failed to predict the phase transformation behavior while others predicted too large or small lattice volumes. Of the fourteen, three functional types, PBEsol, SOGGA, and PBE2, exhibited behaviors consistent with the tetragonal to cubic phase transformation upon heating and they were able to reproduce crystallite volumes within 1.5% of the experimental values. The correlation of XC functional forms and their accuracy in predicting materials properties was discussed.