Noncovalently bound molecular complexes beyond diatom–diatom systems: full-dimensional, fully coupled quantum calculations of rovibrational states

Abstract

The methodological advances made in recent years have significantly extended the range and dimensionality of noncovalently bound, hydrogen-bonded and Van der Waals, molecular complexes for which full-dimensional and fully coupled...

Computing excited OH stretch states of water dimer in 12D using contracted intermolecular and intramolecular basis functions

“…Note that ∆V of paper I does not have the last term. Throughout this paper, as in recent papers using contracted basis functions for VdW complexes, [9,[64][65][66][67]70] we use q A , q B for monomer coordinates and Q = {r 0 , ω A .ω B } for intermolecular coordinates.…”

Mode‐Selective Vibrational‐Tunneling Dynamics in theN=2 Triad of the Hydrogen‐Bonded (HF)2Cluster

“…There has been an extensive debate in the literature using a variety of different simplified quantum dynamical models and also quantum calculations on different full-dimensional potential hypersurfaces (Refs. [35,[58][59][60][61][62][63][64][65]85], see also [86][87][88]). While we shall not attempt here to review this debate in any detail, we can summarize that while the different simplified models provide different magnitudes for the tunneling and also different ordering of the tunneling sublevels, they all predict one level with antisymmetric (B) vibrational symmetry in the N = 2 polyad.…”

Accelerating Anharmonic Spectroscopy Simulations via Local-Mode, Multilevel Methods

“…A suite of methods now exists for this purpose, ranging from variational solvers − , on all or a targeted subset of vibrational modes to more general methods that are often analogues of well-known methods in electronic structure theory. Mean-field methods, such as the vibrational self-consistent field ,− (VSCF) method, can be supplemented by mode-correlation corrections, including perturbation theories (VMP2 , and VDPT2), configuration interaction ,,,,− (VCI), and coupled-cluster theories ,− (VCC); direct correlations from a harmonic reference are also possible. − The success of these methods on reasonably small chemical systemsprovided that spectroscopically accurate potential energy surfaces are employed (typically involving large basis sets and correlated-electron wavefunctions)engenders considerable optimism for their ability to lend insight to the types of systems now accessed with the aforementioned experiments, − including large ion hydrates, biomolecules, and pharmaceuticals. − …”

“…The general applicability of these approaches is severely limited, however, by the practical need for nonlocal (or at least semilocal) representations of the governing potential surface. The ostensibly exponential scaling of such representations has limited these techniques to relatively small molecules/complexes , or small subspaces of larger molecules . One of the standard routes to reducing this complexity is the “ n -mode representation” ( n -MR), ,, which is effectively a many-body expansion in the space of vibrational modes (in selected vibrational coordinates, { q }, for an N -atom system): The 1-body (“1-MR”) terms are composed of one-dimensional cuts along vibrational modes, and although these cuts form intuitive low-dimensional images of anharmonicity, they are often qualitatively incorrectat least in rectilinear displacementsand often even yield the wrong sign of the anharmonicity.…”

“…Infrared and Raman spectroscopies provide detailed glimpses into the behavior of molecules and, implicitly, the potential energy and dipole surfaces that govern their vibrational dynamics. Recent progress in cold-ion sources and action spectroscopies has generated unprecedented insight into ion hydration, hydrogen bonding, and biomolecular structure. − Advanced theory and computational simulations have become critical partners in the interpretation of these modern experiments, ,,,,− and the present investigation aims to address the suitability of a combination of new computational approaches for molecules and clusters of the size accessed by these experiments. In this somewhat expanded Introduction section, the details of these methods will be reviewed, along with the reasons that this pairing of methods is particularly symbiotic for anharmonic simulations of large systems.…”