First-principles investigations on polytypes of BaTiO 3 : Hybrid calculations and pressure dependences

摘要: We report our first-principles investigations on three polytypes of BaTiO3 (BTO): a paraelectric phase with cubic Pm-3m structure and two ferroelectric (FE) phases tetragonal P4mm rhombohedral R3m structures. compared the structural electrical properties BTO obtained by using various approaches: e.g., Hartree-Fock (HF) theory, density functional theory (DFT) local approximation (LDA) or generalized gradient approximations (two GGAs: PWGGA PBE), hybrid functionals HF DFT (B3LYP, B3PW, PBE0). For structure, GGAs reproduced cell volumes, but slightly overestimated c/a ratio. The provided accurate predictions for experimental energy gaps, underestimated dielectric constants. calculated constants were inversely proportional to ratios (or cH/aH ratio structure), irrespective choice. Also, over-estimated polarization could be ascribed super-tetragonality in GGA/hybrid functionals. pressure dependences parameters, fractional atomic displacements, constants, FE polarizations B3PW functional. As was increased, decreased monotonically until it reached zero at critical ∼ 20 GPa both Anomalous behaviors also observed movements structure: δTi, coordinate Ti, showed sign reversal pressures below −8 while maximum −2 then decreasing pressure. However, such effects not increased Such polarizations, together super-tetragonality/super-trigonality, are discussed.