Abstract: The vibrational Stark effect refers to the infrared spectral lines shifting when exposed to an external electric field. This effect has broad applications in modern chemistry. To facilitate the understanding of the vibrational Stark effect, we selected two water molecules for study, i.e., the monomer H₂O and the dimer (H₂O)₂. Using density functional theory calculations, we investigated the influence of an applied electric field directly affects the targeted molecules' geometry, electron density, dipole moment, energy, and vibrational frequencies. As the field strength increases, both H₂O and (H₂O)₂ exhibits spectral shrink, with a redshift of the high-frequency O―H stretching vibrations and a blueshift of the lower-frequency H―O―H bending vibrations. These findings are consistent with previous simulation results reported in the literature. This work provides a straightforward and clear computational case for understanding the vibrational Stark effect.

Key words: Stark effect, Oriented external electric fields, Quantum chemical calculation, Infrared vibration spectrum