Interatomic potentials are determined in the framework of a shell model used to simulate the structural instabilities, dynamical properties, and phase transition sequence of BaTiO₃. The model is developed from first-principles calculations by mapping the potential energy surface for various ferroelectric distortions. The parameters are obtained by performing a fit of interatomic potentials to this energy surface. Several zero-temperature properties of BaTiO₃, which are of central importance, are correctly simulated in the framework of our model. The phase diagram as a function of temperature is obtained through constant-pressure molecular dynamics simulations, showing that the non-trivial phase transition sequence of BaTiO₃ is correctly reproduced. The lattice parameters and expansion coefficients for the different phases are in good agreement with experimental data, while the theoretically determined transition temperatures tend to be too small.