Lattice vibration, heat capacity and vibration entropy of single-layer hexagonal-BN

The phonon spectrum of zigzag h-BN nanoribbons with the edges passivated by hydrogen atoms under tensile strain along the axis direction were calculated by first-principle calculations. It is found that the uniaxial strain can lead to a narrow frequency range of lattice vibration modes. But it hardly affects the two highest frequency modes due to the vibration of B-H or N-H bonds. In particular, the strain usually promotes the softening of phonon modes. It means that more phonons should be activated at a given temperature. This may result in the changes of thermal properties, such as, heat capacity and vibration entropy.