Size Effect of Piezoelectricity in ZnO Nanowires: A First-Principles Study

Piezoelectric properties of ZnO nanowires orientated along [0001] are investigated via density functional theory (DFT). A new method to calculate the volume of nanowires was proposed, which is crucial to the value of piezoelectric coefficients. Results show that the axial effective piezoelectric coefficients are 29.99 Cm-2, 25.93 Cm-2, 22.82 Cm-2 for ZnO nanowires with diameters of about 0.6 nm, 1.2 nm, 1.8 nm, which are considerably larger than that of the bulk (20.19Cm-2). It is found that the change in volume during the strain played a dominated role in size effects. This work helps to gain a deeper understanding of the piezoelectric size effects in ZnO nanowires.