FIRST-PRINCIPLES STUDY OF PIEZOELECTRICITY IN TETRAGONAL PBTIO3

The e(33) component of the piezoelectric strain tensor in tetragonal P bTiO3 was studied by an all-electron ab initio method, and was found t o be in good agreement with the experimental piezoelectric stress cons tant of high quality twin-free single PbTiO3 crystals. Equations of th e density functional theory were solved within the general gradient ap proximation (GGA) using the general potential linearized augmented pla ne-wave local orbital (LAPW+LO) method. Macroscopic polarization value s necessary to calculate the piezoelectric coefficient and elements of the Born effective charge tensors were determined via finite differen ces using the geometric phase formulation. In this approach, bulk quan tities are expressed as the property of the phase of the wavefunction in terms of a Barry connection. The e(33) component of the piezoelectr ic tensor, i.e. the change in polarization with strain, was extracted from results of groundstate Berry's phase calculations performed on un its cells of different strains and volumes, We found that in PbTiO3 th e large intrinsic piezoelectric response is mainly due to strong coupl ing between macroscopic strain and internal microscopic strain, giving the value of 3.23 C/m(2) for the e(33) modulus.