, where i runs over all the atoms of a particular species in the supercells, c is the lattice parameter, |e| is the magnitude of an electron's charge, Z 33 (i) is the BEC of i-th atom, u 3 is the fractional position of an atom along c-direction, and Ω is the volume of the supercells. Surprisingly, we find that contributions from B and N atoms dominate in e ion 33 (see Table ), suggesting that negative piezoelectricity mainly originates from ionic movement of B and N, and the dopant atoms (Al or Ga) are responsible for breaking the inversion symmetry of bulk h-BN to induce piezoelectricity. Interestingly, we also observe that almost half of the B or N atoms shows a positive du3 dη3 , i.e. they move in the positive c-direction in response to the elongation of c lattice parameter, for which η 3 is positive, while the other B/N atoms move in the negative cdirection and show negative du3 dη3 . This can be attributed to the role of the Al/Ga atom as a linker connecting two h-BN planes. The Z 33 and the du3 dη3 of each atom in the supercells are provided in Supplementary Information.