Theory
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See the following papers.

* W. Zhong, David Vanderbilt, and K. M. Rabe. “First-principles theory of ferroelectric phase transitions for perovskites: The case of BaTiO3 ,” Phys. Rev. B, 52, 6301 (1995).

* "Ewald summation for ferroelectric perovksites with charges and dipoles”, by D. Wang, J. Liu, J.  Zhang, S. Raza, X. Chen, and C.-L. Jia.