-------------------------------------------------------------------------------- ### Interplay between Ferroelectricity and Metallicity in BaTiO3 -------------------------------------------------------------------------------- V. F. Michel, T. Esswein, N. A. Spaldin -------------------------------------------------------------------------------- #### Abstract: We explore the interplay between ferroelectricity and metallicity, which are generally considered to be contra-indicated properties, in the prototypical ferroelectric barium titanate, BaTiO3. Using first-principles density functional theory, we calculate the effects of electron and hole doping, first by introducing a hypothetical background charge, and second through the introduction of explicit impurities (La, Nb and V for electron doping, and K, Al and Sc for hole doping). We find that, apart from a surprising increase in polarization at small hole concentrations, both charge-carrier types decrease the tendency towards ferroelectricity, with the strength of the polarization suppression, which is different for electrons and holes, determined by the detailed structure of the conduction and valence bands. Doping with impurity atoms increases the complexity and allows us to identify three factors that influence the ferroelectricity: structural effects arising largely from the size of the impurity ion, electronic effects from the introduction of charge carriers, and changes in unit-cell volume and shape. A competing balance between these contributions can result in an increase or decrease in ferroelectricity with doping. -------------------------------------------------------------------------------- All calculations were performed using the VASP code (version 5.4.4), with recommended projector-augmented wave potentials and the PBEsol exchange-correlation functional. The main folder contains input and the most relevant output files for all calculations presented in the paper. The subfolders follow the structure of the paper. Note that the folders named "SC" correspond to self-consistent field calculations. The presented charge densities were calculated as "Band decomposed charge density calculations", as named in VASP (www.vasp.at/wiki/index.php/Band_decomposed_charge_densities, accessed on April 2021).