Hydrogen Bond In Water Dimer Research Articles

Zero-point fluctuation of hydrogen bond in water dimer from ab initio molecular dynamics**Project supported by the National Natural Science Foundation of China (Grant Nos. 11974136 and 11674123).

Dynamic nature of hydrogen bond (H-bond) is central in molecular science of substance transportation, energy transfer, and phase transition in H-bonding networks diversely expressed as solution, crystal, and interfacial systems, thus attracting the state-of-the-art revealing of its phenomenological edges and sophisticated causes. However, the current understanding of the ground-state fluctuation from zero-point vibration (ZPV) lacks a firm quasi-classical base, concerning three basic dimensions as geometry, electronic structure, and interaction energy. Here, based on the ab initio molecular dynamics simulation of a ground-state water dimer, temporally separated fluctuation features in the elementary H-bond as the long-time weakening and the minor short-time strengthening are respectively assigned to two low-frequency intermolecular ZPV modes and two O–H stretching ones. Geometrically, the former modes instantaneously lengthen H-bond up to 0.2 Å whose time-averaged effect coverages to about 0.03 Å over 1-picosecond. Electronic-structure fluctuation crosses criteria’ borders, dividing into partially covalent and noncovalent H-bonding established for equilibrium models, with a 370% amplitude and the district trend in interaction energy fluctuation compared with conventional dragging models using frozen monomers. Extended physical picture within the normal-mode disclosure further approaches to the dynamic nature of H-bond and better supports the upper-building explorations towards ultrafast and mode-specific manipulation.

Hydrogen bonding characterization in water and small molecules.

The prototypical hydrogen bond in water dimer and hydrogen bonds in the protonated water dimer, in other small molecules, in water cyclic clusters, and in ice, covering a wide range of bond strengths, are theoretically investigated by first-principles calculations based on density functional theory, considering not only a standard generalized gradient approximation functional but also, for the water dimer, hybrid and van der Waals corrected functionals. We compute structural, energetic, and electrostatic (induced molecular dipole moments) properties. In particular, hydrogen bonds are characterized in terms of differential electron density distributions and profiles, and of the shifts of the centres of maximally localized Wannier functions. The information from the latter quantities can be conveyed to a single geometric bonding parameter that appears to be correlated with the Mayer bond order parameter and can be taken as an estimate of the covalent contribution to the hydrogen bond. By considering the water trimer, the cyclic water hexamer, and the hexagonal phase of ice, we also elucidate the importance of cooperative/anticooperative effects in hydrogen-bonding formation.

Effect of the Hydrogen Bond in Photoinduced Water Dissociation: A Double-Edged Sword.

Photoinduced water dissociation on rutile-TiO2 was investigated using various methods. Experimental results reveal that the water dissociation occurs via transferring an H atom to a bridge bonded oxygen site and ejecting an OH radical to the gas phase during irradiation. The reaction is strongly suppressed as the water coverage increases. Further scanning tunneling microscopy study demonstrates that hydrogen bonds between water molecules have a dramatic effect on the reaction. Interestingly, a single hydrogen bond in water dimer enhances the water dissociation reaction, while one-dimensional hydrogen bonds in water chains inhibit the reaction. Density functional theory calculations indicate that the effect of hydrogen bonds on the OH dissociation energy is likely the origin of this remarkable behavior. The results suggest that avoiding a strong hydrogen bond network between water molecules is crucial for water splitting.

Is the Hydrogen Bond in Water Dimer and Ice Covalent?

The changes in charge and momentum distributions upon forming a hydrogen bond in the water dimer are examined. The computed Compton profile anisotropies show the same oscillations as were observed for solid ice. These oscillations are already found when the unperturbed orbitals of the water monomers are used to construct a Slater determinant for the dimer. Hence we conclude that the oscillations are irrelevant to the discussion of the covalent character of the bond. Rather they just reflect the result of antisymmetrizing the product of monomer wave functions. In fact, at the oxygen−oxygen distance in ice, the calculations indicate a net antibonding contribution to energy from overlap effects.

Proton potential and properties of hydrogen bond

1. A model potential of the hydrogen bond in water dimer can be represented in the form of a sum of long-range charge-dipole attraction, short-range attraction, and exponential repulsion. Here, by a proper selection of parameters, a good description can be given for the dependence of the bond energy on the interatomic distance R. 2. The presence of a finite zero energy of the proton and the coupled character of the atomic vibrations in the H2O molecule lead to a certain redetermination of the parameters of the model potential V(r, R). In particular, the depth of the potential well for the O−H bond increases, as does the parmeter C of Coulomb attraction. 3. The relatively low-lying excited quantum levels of the proton and its analytical wave function can be obtained with an adequate degree of accuracy by means of a simplified potential V(r, R) that has the from of a Morse potential with parameters depending on the interatomic distance R. This simplified potential gives a correct reproduction of the form of V(r, R) close to the equilibrium position of the protonr≈r0. 4. The dependence of the bond energy E(R) has the required form, with the radius of action of the forces of the hydrogen bond and their magnitude becoming slightly greater with increasing sequence number of excitation. In particular, the work of shortening the distance R from ∞ to Ro for the first excited state amounts to about 45% of the excitation energy.

Molecular orbital calculations on distorted hydrogen bonds in the water dimer

CNDO/2 MO calculations have been carried out to investigate the effect of distortions of the hydrogen bond in the open water dimer. Linear dimers of water are more stable when the O–H vector is not directed towards the lonepair orbital of the donor oxygen atom, the stability being maximum when the hydrogen is in between the two lonepair orbitals. Bending the hydrogen bond in the water dimer markedly decreases hydrogen-bond energy and increases the dimer energy when the angle of bend is greater than ca. 30°.