Raman activity of sp3 carbon allotropes under pressure: A density functional theory study

Raman spectroscopy is a powerful tool to study the intrinsic vibrational characteristics of crystals, and, therefore, it is an adequate technique to explore phase transitions of carbon under pressure. However, the diamond-anvil cell, which is used in experiments to apply pressure, appears as a broad intense feature in the spectra. This feature lies, unfortunately, in the same range as the principal modes of recently proposed sp3 carbon structures. As these modes are hard to distinguish from the diamond cell background, we analyze all Raman-active modes present in the sp3 carbon structures in order to find detectable fingerprint features for an experimental identification.