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Keywords:

  • first-principles DFT calculations;
  • phonons;
  • photovoltaic materials

Frozen-phonon calculations on structurally related tetragonal Cu2ZnSnSe4 and monoclinic Cu2SnSe3 reveal similarities in the shape and overall composition of vibration spectra, but also marked deviations in the frequency and nature of certain modes. These deviations are often induced by different connectivity on the cation sublattice and can be traced to a specific structural motive. In the analysis of vibrations, a variety of projection schemes applied to phonon eigenvectors calculated within the density functional theory by the SIESTA method help to reveal different aspects in vibration modes, e.g., strength of particular in-phase atomic movements, or attribution of specific vibration modes to particular irreducible representations of the space group.