Abstract:An exactly solvable model of the linear interaction of molecular vibrations with the electronic states of molecules is utilized to describe the intensity distributions in band systems observed in the ultraviolet photoelectron and ultraviolet absorption spectra of C6H6 and C6D6. From this analysis, the linear coupling constants describing the vibration-induced energy shifts of the 1e1g(π), 3e2g(σ), and 3a1g(σ) one-electron orbitals and of the 1B2u excited state are determined. These coupling constants also are … Show more
We present a method for accelerating GW quasi-particle (QP) calculations. This is achieved through the introduction of optimal basis sets for representing polarizability matrices. First the real-space products of Wannier like orbitals are constructed and then optimal basis sets are obtained through singular value decomposition. Our method is validated by calculating the vertical ionization energies of the benzene molecule and the band structure of crystalline silicon. Its potentialities are illustrated by calculating the QP spectrum of a model structure of vitreous silica. Finally, we apply our method for studying the electronic structure properties of a model of quasi-stoichiometric amorphous silicon nitride and of its point defects.
We present a method for accelerating GW quasi-particle (QP) calculations. This is achieved through the introduction of optimal basis sets for representing polarizability matrices. First the real-space products of Wannier like orbitals are constructed and then optimal basis sets are obtained through singular value decomposition. Our method is validated by calculating the vertical ionization energies of the benzene molecule and the band structure of crystalline silicon. Its potentialities are illustrated by calculating the QP spectrum of a model structure of vitreous silica. Finally, we apply our method for studying the electronic structure properties of a model of quasi-stoichiometric amorphous silicon nitride and of its point defects.
“…What are the selection rules imposed on the coupling constants? These questions have been discussed by Lipari et al 21 whose symmetry arguments show that only totally symmetric molecular vibrational modes couple linearly to nondegenerate molecular orbitals. If ionized states of a molecule are nondegenerate, the forces, Qץ/ץ( i ) N and Qץ/ץ( ␣ ) N , possess molecular symmetry.…”
A basic theoretical structure for mechanochemical transformations based on prior models for solid-state reactions and HOMO-LUMO ͑highest occupied molecular orbital-lowest unoccupied molecular orbital͒ gap closing produces the concept of distortion-induced molecular electronic degeneracy ͑DIMED͒ of the highest occupied and lowest unoccupied molecular orbitals of an energetic molecule. Both intermolecular and intramolecular charge transfer are involved. The resulting distortion-induced local instability, a mechanochemical effect, leads to chemical transformations and can be analyzed by renormalization of the molecular hardness through the molecular deformation energy. Linear combinations of normal modes are shown to be useful for description of the mechanically induced reaction path. Numerical calculations for the RDX ͑hexahydro-1,3,5-trinitro-1,3,5-triazine͒ molecule are used to construct a path for initiation of a reaction by shock. They show the breaking of a single N-N bond as the primary step. DIMED is shown to be a kind of ''inverse Jahn-Teller effect'' leading to the general conclusion that distortion-induced instabilities and mechanically induced reactions require some, but not necessarily complete, HOMO-LUMO gap closure. This indicates that large local strains due to defects or cracks will contribute to DIMED. The DIMED concept, because of its generality, has wide applicability in solid-state chemistry.
“…105,132,133,147,148 Unequivocally, the C-H stretching mode ν 15 has been found to have negligible JT activity in the X 2 E 1g ground state, while the other three degenerate modes are found to be moderately JT active. Also, the ordering D 18 > D 16 > D 17 for the linear coupling parameters D i = k 2 i /2ω 2 i (i =16-18) is in mutual agreement in the literature.…”
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