More than 30 years ago two groups independently identified a problem in the calculation of
the out-of-plane bending (OPB) vibrational frequencies for the ethylene molecule using …

We propose an approximation to the vibrational coupled-cluster method (VCCM) to describe
the CH-stretching region of the vibrational spectrum of large molecules. The vibrational …

The challenges associated with the out-of-plane bending problem in multiply-bonded
hydrocarbon molecules can be mitigated in quartic force field analyses by varying the step …

We present a detailed study on the role of atomic orbitals in the unphysical description of the
out-of-plane bending (OOPB) vibrations with the MP2 method. The anharmonicities of the …

In this work, we report anomalous descriptions of bending modes of the carbon–carbon
double bonded molecules with double hybrid density functional theories. The harmonic …

The nature of the wavefunctions associated with the final states in the CH stretching region
of several medium sized molecules is analysed. The number of optically bright transitions is …

We propose a perturbative approximation to the vibrational coupled cluster method in
bosonic representation to reduce the cost of calculating the cluster matrix elements by …

A theory for calculating vibrational energy levels and infrared intensities is developed in the
equation of motion framework at the random phase approximation level. The vibrational …