I'm new to the Quantum ESPRESSO package. There are articles outlining the procedure of indirectly simulating the P-E loop of piezo-electric materials via Berry phase calculations.One procedure is indicated below:
"Perform a set of finite field calculations and plot the stress vs applied electric field, then the slope at zero field gives you the piezoelectric coefficients. For a more elegant solution, you can check the following paper: S. de Gironcoli et al. PRL 62, 2853 (1989)"
But I couldn't find any explicit step-wise procedure for simulating the P-E loop. So any help regarding the topic will be good.