Strain tuning effects on phonon coupling in energy-related materials

Abstract

Despite inelastic neutron scattering has been extremely successful in the studies of lattice dynamics of anharmonic materials, theory has lagged behind in the context of vibrations. In this presentation, I will discuss about the phonon coupling calculations of different energy-related materials based on density functional theory and molecular dynamics simulations. I will discuss about the pressure tuning effects on the phonon coupling in perovskite MAPbI3, which exhibits outstanding optoelectronic properties, but its thermal instability still hinders practical applications. Using the mode decomposition technique, we obtain the lifetimes of different phonon modes, which are found to be very sensitive to compression. A small hydrostatic pressure of several kbar can lead to a considerable change of the phonon lifetime, originating from the four-fold rotation of the MA+ cations around the C-N axis. I will also discuss about the anomalous phonon spectral features of PbTe and SnTe, and the corresponding pressure effects obtained from first-principles calculations. The anomalous phonon spectral features are believed to be related to the excellent thermoelectric properties of these binary compounds. Lastly, the phonon spectra of strained graphene obtained from anharmonic lattice dynamics calculations will be discussed. Although graphene has been studied extensively over the past decades, there are still ambiguities regarding its mechanical failure mechanisms. Our calculations provide a more in-depth understanding of the phonon-mediated failure of graphene.