First principles-based calculation of the electrocaloric effect in BaTiO$_3$: comparison between direct and indirect methods

摘要

We use molecular dynamics simulations for a first principles-based effectiveHamiltonian to calculate two important quantities characterizing theelectrocaloric effect in BaTiO$_3$, the adiabatic temperature change $\Delta T$and the isothermal entropy change $\Delta S$, for different electric fieldstrengths. We compare direct and indirect methods to obtain $\Delta T$ and$\Delta S$, and we confirm that both methods indeed lead to identical resultprovided that the system does not actually undergo a first order phasetransition. We also show that a large electrocaloric response is obtained forelectric fields beyond the critical field strength for the first order phasetransition. Furthermore, our work fills several gaps regarding the applicationof the first principles-based effective Hamiltonian approach, which representsa very attractive and powerful method for the quantitative prediction ofelectrocaloric properties. In particular, we discuss the importance ofmaintaining thermal equilibrium during the field ramping when calculating$\Delta T$ using the direct method within a molecular dynamics approach.