Anharmonic Stretching Frequencies of Local OH Bonds in Water Dimer: Ab Initio Potential Energy and Discrete Variable Representation

Abstract

The fundamental and first overtone transition frequencies of local OH bonds of the hydrogen bond donor molecule in a water dimer were calculated by numerically solving one-dimensional Schrödinger equation with anharmonic potential energies obtained by ab initio quantum chemical methods at the near basis set limit. Among the various ab initio theories considered, the coupled cluster theory is found to give the most accurate frequencies in comparison with experiments, and the quadratic configuration interaction theory exhibits a similar accuracy. The calculated frequencies of the free and hydrogen-bonded OH bonds excellently agree with experimental frequencies of a gaseous dimer. It was found that the anharmonicity of the fundamental transition frequency is influenced by hydrogen bonding to a larger extent than the anharmonicity of the 1-2 transition frequency.

Evaluating the Role of Anharmonic Vibrations in Zeolite β Materials

“…For instance, an anharmonic mode described by a Morse potential would be “softer” than the harmonic approximation in one direction but “harder” in the other, as depicted in Figure , which would lead to cancellation in the scaling factor producing values close to unity; however, we believe the discrepancy observed here may also arise through application of different methods to sample energy landscapes. Pronounced anharmonicity could occur from the aiMD approach through the evaluation of atomic displacements that sample significant variation in the local environment, and hence interatomic interactions around the Brønsted acid site, which themselves are known to increase anharmonicity , compared to the limited sampling along Cartesian axes that may be used to derive scaling factors for the harmonic approximation. Our results demonstrate that anharmonicity is dependent on chemical environment, and therefore another implication is the potential inadequacy of scaling factors derived for application to results via the harmonic approximation, if these scalars are then applied for the same bond types in different environments.…”

A strategy to compute quantum chemical potential energies of inhomogeneous OH bonds in water molecules

“…9 Since the signal of vibrational nonlinear spectroscopies reflects the characteristics of vibrational anharmonicity, 10 this property should be accurately incorporated into the theories for quantitative connection between experiments and theories. The anharmonicity is also influenced by the intermolecular interaction including hydrogen bonding 11 and therefore its magnitude is inhomogeneously distributed and varies with molecular environment.…”