Electron Donation in the Water-Water Hydrogen Bond

An energy decomposition and charge-transfer (CT) analysis was carried out to study the intermolecular CT effects in the hydrogen bond between two water molecules by using density functional calculation. The energy-decomposition analysis (EDA) and charge-transfer analysis (CTA) used for the study are based on absolutely localized molecular orbitals (ALMOs). It was observed that the EDA and CTA are suitable for separating CT from frozen density and polarization interactions. It was also found that the CT effects, frozen density interactions, and polarization can make a significant impact on hydrogen bonding. The CT is found to be insensitive to intermolecular rotation of the water molecules. Complementary occupied-virtual pairs (COVPs) can provide a view of the electron-donating orbital in the water dimer.