Perspective: Accurate ro-vibrational calculations on small molecules

Abstract

In what has been described as the fourth age of quantum chemistry, variational nuclear motion programs are now routinely being used to obtain the vibration-rotation levels and corresponding wavefunctions of small molecules to the sort of high accuracy demanded by comparison with spectroscopy. In this perspective, I will discuss the current state-of-the-art which, for example, shows that these calculations are increasingly competitive with measurements or, indeed, replacing them and thus becoming the primary source of data on key processes. To achieve this accuracy ab initio requires consideration of small effects, routinely ignored in standard calculations, such as those due to quantum electrodynamics. Variational calculations are being used to generate huge lists of transitions which provide the input for models of radiative transport through hot atmospheres and to fill in or even replace measured transition intensities. Future prospects such as the study of molecular states near dissociation, which can provide a link with low-energy chemical reactions, are discussed. Published by AIP Publishing. [http://dx

The Hunt for Elusive Molecules: Insights from Joint Theoretical and Experimental Investigations

“…For small molecules with fewer than four or five atoms, numerically exact variational nuclear motion calculations yield high accuracy rovibrational energies and spectroscopic constants limited only by the underlying potential energy surface. [56] One example of such a calculation from our work below is the floppy SiCSi molecule.…”

Non-adiabatic mass correction to the rovibrational states of molecules: Numerical application for the H2+ molecular ion

“…Rovibrational computations can be efficiently performed (see for example Refs. [34,35]), if the laboratory-fixed Cartesian coordinates are replaced with a physically motivated (curvilinear) coordinate set, ξ. This physically motivated set includes a set of internal coordinates that are well suited to describe the internal motions (vibrations), three orientation angles which describe the orientation of the body-fixed frame with respect to the laboratory frame (rotations), and three coordinates which describe the translation of the center of mass (translations).…”

The any particle molecular orbital approach: A short review of the theory and applications

“…[81] Geometric isotope effects (GIEs), on the other hand, can be retrieved by solving a nuclear Schrödinger equation that considers the anharmonicity of the nuclear potential. [82][83][84] These calculations are usually carried out employing the vibrational self-consistent field method [85] or grid based approaches such as the discrete variable representation. [86][87][88][89] Alternatively, GIEs can be analyzed performing path integral molecular dynamics simulations.…”