Fully Coupled Quantum Treatment of Nanoconfined Systems: A Water Molecule inside a Fullerene C₆₀

Abstract

We implemented a systematic procedure for treating the quantal rotations by including all translational and vibrational degrees of freedom for any triatomic bent molecule in any embedded or confined environment, within the MCTDH framework.Fully coupled quantum treatments were employed to investigate unconventional properties in nanoconfined molecular systems. In this way, we facilitate a complete theoretical analysis of the underlying dynamics, that enables to compute the energy levels and the nuclear spin isomers of a single water molecule trapped in a C 60 fullerene cage.The key point lies on the full 9D description of both nuclear and electronic degrees of freedom, as well as a reliable representation of the guest-host interaction. The presence of occluded impurities or inhomogeneities due to noncovalent interactions in the inter-fullerene environment could modify aspects of the potential, causing significant * To whom correspondence should be addressed coupling between otherwise uncoupled modes. Using specific n-mode model potentials, we obtained splitting patterns, that confirm the effects of symmetry breaking observed by experiments in the ground ortho-H 2 O state. Further, our investigation reveals that the first rotationally excited states of the encapsulated ortho-and para-H 2 O have also raised their three-fold degeneracy. In view of the complexity of the problem our results highlight the importance of accurate and computational demanding approaches for building up predictive models for such nanoconfined molecules.

Encapsulation of a Water Molecule inside C60 Fullerene: The Impact of Confinement on Quantum Features

“…In this study, the methodology already developed in ref ( 22 ) is exploited for any light–heavy–light encapsulated molecule to describe the quantum mechanical features of H 2 O@C 60 endohedral fullerene. We demonstrate the robustness of the method on systems that cannot be described through simple models by carrying out high-accuracy calculations of the molecular levels of the system.…”

“…In previous works of the H 2 O@C 60 system, 22 , 44 , 60 the potential term, V , was built up employing the sum-of-potentials approach, with the intermolecular interaction between the water molecule and C 60 , plus the intramolecular water potential, . The V H 2 O–C 60 potential was generated as a sum over the H 2 O–C pairwise interactions, modeled with the H–C and O–C Lennard-Jones (LJ) 12-6 potentials adjusted to DFT-SAPT ab initio graphene–water reported in ref ( 39 ), while the water monomer potential was taken from ref ( 61 ).…”

Exploring the Properties of H2O@C60 with the Local Second‐Order Møller‐Plesset Perturbation Theory: Blue or Red Shift in C60 and H2O Fundamentals to Expect?

“…On the other hand, another method employing 9D vibrational Hamiltonian for H 2 O@C 60 still predicts blue shifts of all H 2 O frequencies on account of limitations of the applied model ( i. e ., by treating host as a rigid entity and utilizing rather imprecise potential energy surface) [36] . Even the very recent full 9D results [43,44] based on the multiconfiguration time‐dependent Hartree approach suffer from the same deficiency.…”

Unraveling the Origin of Symmetry Breaking in H2O@C60 Endofullerene Through Quantum Computations

“…Up to date, a variety of theoretical models and scenarios have been elaborated [16,[25][26][27][28][29] to explore these experimental observations. In a series of studies, Bačić and co-workers [26,28,30,31] have performed 6D and 9D quantum calculations on translational-rotational and vibrational states of the H 2 O@C 60 system, while in order to treat the symmetry-lowering interactions, they have introduced electrostatic models involving dipole-dipole interactions between two neighbor H 2 O@C 60 , or quadrupole interactions between the charge densities of an encapsulated H 2 O molecule in a central C 60 cage surrounded by twelve empty ones.…”