Electrocaloric effect in bulk and low-dimensional ferroelectrics from first principles

First-principles-based effective Hamiltonians are combined with nonequilibrium molecular dynamics to determine the electric-field-induced change in temperature in ferroelectrics. As a result, (i) the applied field can be ac in nature with a wide frequency range, (ii) bulks and nanostructures (with homogeneous or highly inhomogeneous dipolar configurations) can be investigated, and (iii) the influence of various phenomena on the electrocaloric effect can be revealed. This scheme yields an electrocaloric coefficient in excellent agreement with measurement and that strongly depends on the field-induced variation of volume in Pb(Zr_1-xTiₓ)O₃ bulks. An unusual phenomenon is also reported in dots under ac fields.