Sum-frequency vibrational spectroscopy of D ₂ O at interfaces

Interfacial water governs a wide range of fundamental processes across biological, chemical, and materials systems. This study leverages the mixed quantum/classical method and artificial neural network-based molecular dynamics (MD) simulations to investigate the orientation and sum-frequency vibrational spectroscopy (SFVS) of D2O at interfaces. The results demonstrate that the SFVS signal is dominated by the electric dipole term. The electric quadrupole effect, while of secondary importance, is still non-negligible, and the magnetic dipole contribution is comparatively very small. These multipole interactions together rationalise the absence of the controversial low-frequency positive peak in the OD stretching region of SFVS. Such insights advance our fundamental understanding of aqueous interfaces.