XVIth International Workshop on
Quantum Systems in
Chemistry and Physics
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Piezoelectricity
Michael Springborg and Bernard Kirtman
Physical and Theoretical Chemistry, University of Saarland, Campus B2.2, 66123 Saarbrücken, Germany
Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, U.S.A.
Piezoelectricity results from a coupling between responses to mechanical and electric perturbations. Conveniently, it can be studied theoretically by analysing the change in the dipole moment due to strain or stress. However, whereas the definition of the operator for the dipole moment for any finite system, independent of its size, is trivial, it is only within the last 1 - 2 decades that the expressions for the equivalent operator in the independent-particle approximation for the infinite and periodic system have been proposed. We indicate how these expressions can be derived and which approximations are involved. We demonstrate that the so called branch dependence of the dipole moment per unit for the infinite and periodic system is related to physical observables in contrast to what often is assumed. Finally, again in contrast to common assumptions, we argue that the dipole moment per unit may change branch abruptly. This is related to the finding that piezoelectric properties depend both on the terminations and on the shape of the samples of interest even for samples with size well above the thermodynamic limit.


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