First-Principle Calculation of Elastic Compliance Coefficients for BiFeO3

The elastic compliance coefficients of PbTiO3 with/without geometric optimization are firstly calculated by using density-functional theory (DFT) under different exchange correlation functions. It is found that the best results are not obtained by LDA/CA-PZ and optimized structure although these induce the nearest lattice constants to experimental ones, however, the results of PbTiO3 without geometry optimization under GGA/PW91 function are in great consistent with the experimental data. Based on the same calculating method of PbTiO3, the elastic compliance coefficients for BiFeO3 are obtained. And the data are compared with previous results predicted by fitting experimental data to Landau-type phenomenological theory, which possessing the difference of an order of magnitude with our data.