Vibrational spectroscopy

Vibrational spectroscopy is an ideal tool to probe the complex structure of hydrogen bonded systems, in particular ice, water and aqueous solutions. However, the interpretation of experimental spectra is usually not straightforward, due to complex spectral features associated with different bonding configurations present in these systems. Therefore, accurate theoretical predictions are required to assign spectral signatures to specific structural properties and hence to fully exploit the potential of vibrational spectroscopies.

We develop and use first-principles electronic structure methods for the simulation of vibrational spectra of aqueous systems, including IR, Raman and sum frequency generation spectra, at ambient and extreme conditions.

Raman, Infrared & SFG Spectra of Aqueous Systems

SFG

Using first principles molecular dynamics and both semi-local and hybrid functionals, we computed vibrational spectra of liquid water. In particular, we computed Raman and IR spectra and found a satisfactory agreement with experiment and we devised a systematic strategy to analyze the Raman intensities, which is of general applicability to molecular solids and liquids, and it is based on maximally localized Wannier functions and effective molecular polarizabilities. In addition we developed a first-principles framework to compute sum-frequency generation (SFG) vibrational spectra of semiconductors and insulators, that we applied to ice. The method includes the effect of electric field gradients at surfaces and quadrupolar contributions, thus enabling the verification of the dipolar approximation, whose validity determines the surface specificity of SFG spectroscopy.