Field-induced structure transformation in electrorheological solids.

We have computed the local electric field in a body-centered tetragonal (bct) lattice of point dipoles via the Ewald-Kornfeld formulation, in an attempt to examine the effects of a structure transformation on the local-field strength. For the ground state of an electrorheological solid of hard spheres, we identified a different structure transformation from the bct to the face-centered cubic (fcc) lattices by changing the uniaxial lattice constant c under the hard-sphere constraint. In contrast to the previous results, the local field exhibits a nonmonotonic transition from bct to fcc. As c increases from the bct ground state, the local field initially decreases rapidly towards the isotropic value at the body-centered cubic lattice, decreases further, reaching a minimum value and increases, passing through the isotropic value again at an intermediate lattice, reaches a maximum value and finally decreases to the fcc value. An experimental realization of the structure transformation is suggested. Moreover, the change in the local field can lead to a generalized Clausius-Mossotti equation for the bct lattices.