Strong static and dynamic Jahn–Teller and pseudo-Jahn–Teller effects in niobium tetrafluoride

Abstract

We present a first-principles study of the static and dynamic aspects of the strong Jahn–Teller (JT) and pseudo-JT (PJT) effects in niobium tetrafluoride, NbF4, in the manifold of its electronic ground state, 2E, and its first excited state, 2T2. The complex topography of the full-dimensional multi-sheeted adiabatic JT/PJT surfaces is analyzed computationally at the complete-active-space self-consistent-field (CASSCF) and multireference second-order perturbation levels of electronic structure theory, providing a detailed characterization of minima, saddle points, and minimum-energy conical intersection points. The calculations reveal that the tetrahedral (Td) configuration of NbF4 undergoes strong JT distortions along the bending mode of e symmetry, yielding tetragonal molecular structures of D2d symmetry with Td → D2d stabilization energies of about 2000 cm−1 in the X̃2E state and about 6400 cm−1 in the Ã2T2 state. In addition, there exists strong X̃2E−Ã2T2 PJT coupling via the bending mode of t2 symmetry, which becomes important near the crossing seam of the X̃2E and Ã2T2 potential energy surfaces. A five-state five-mode JT/PJT vibronic-coupling Hamiltonian is constructed in terms of symmetry-invariant polynomial expansions of the X̃2E and Ã2T2 diabatic potential energy surfaces in the e and t2 bending coordinates. The parameters of the Hamiltonian are determined by a least-squares fit of its eigenvalues to the CASSCF ab initio data. The vibronic spectra and the time evolution of adiabatic electronic population probabilities are computed with the multi-configuration time-dependent Hartree method. The complexity of the spectra reflects the effects of the exceptionally strong E × e and T2 × e JT couplings and (E + T2) × (e + t2) PJT coupling. The time evolution of the populations of the adiabatic electronic states after the initial preparation of the Ã2T2 state reveals the femtosecond nonadiabatic dynamics through a multidimensional seam of conical intersection. These results represent the first study of the static and dynamical JT/PJT effects in the X̃2E and Ã2T2 electronic states of NbF4.

Vaporization Processes and Accurate Molecular Structure of a Number of Organic and Inorganic Compounds Promising for Use in Technologies Involving the Gas Phase

“…Эти методы позволяют учитывать в равной мере сильные вибронные и спин-орбитальные взаимодействия, а также нежесткие, с большой амплитудой движения ядерной подсистемы, характерные для молекул этого класса. Такого рода исследования были выполнены, например, для молекул тетрафторидов ванадия, ниобия и тантала MF4 (M = V, Nb, Ta) [130][131][132]. Они продемонстрировали определяющий вклад эффектов и псевдоэффектов Яна-Теллера в свойства низколежащих электронных состояний этих молекул и в их спектроскопические характеристики.…”

Quantum dynamics with ab initio potentials

“…Jahn-Teller and similar symmetry-determined vibronic coupling problems can also be treated in this way. Vasilyev et al 42 set up and study a five state, nine mode model of Niobium tetrafluoride to look at the importance of Jahn-Teller and pseudo-Jahn-Teller coupling in its photo-excited dynamics. Viel et al 43 study the Jahn-Teller effect in the photodetachment of the nitrate anion (NO 3 − ), extending the standard vibronic coupling model to higher orders, and building in the full symmetry of the problem, resulting in a full spectral assignment for this atmospherically relevant molecule.…”

Angular Jahn–Teller Effect and Photoluminescence of the Tetrahedral Coordinated Mn2+ Activators in Solids–A First-Principles Study

“…The transition metal molecules or clusters have been modeled by quantum chemistry calculations, − and various improvements have been reported to deal with the problem induced by carving a finite cluster from the bulk, which often involves cutting metal-linker bonds, and may lead to charged clusters and truncation artifacts, and thus the results may depend sensitively on the choice of the cluster. − On the other hand, the calculations based on density functional theory with the periodic supercell formalism have been successfully applied in the study of the stabilization and luminescence of activator centers, such as Ce 3+ , Bi 3+ , Mn 3+ , and Mn 4+ . For the excited states of the multielectron d 5 system in the framework of density functional theory, the spin contamination is a problem in particular to overcome, , which could especially be challenging for the excited states in tetrahedral coordinations due to the much weaker ligand-field splitting than the cases of octahedral or cubic coordinations.…”