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  • 11
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 117 (1995), S. 6921-6926 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 8514-8520 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We discuss the Jahn–Teller effect and possible superconductivity in negatively charged [18]annulene, (CH)18, which is an interesting molecular system with a highly symmetric D6h geometry in the neutral state. Electron–phonon coupling constants in model one-dimensional crystals of (CH)18−, (CH)183−, (CD)18−, and (CD)183− are calculated and analyzed using the B3LYP density functional method of Becke and Lee, Yang, and Parr. The lowest two frequency modes (116 cm−1 and 405 cm−1) causing distortions of the C–C framework of [18]annulene and the highest frequency mode (3201 cm−1) of C–H stretching appear to give significant electron–phonon coupling constants. The computed coupling constants of the monoanion are larger than those of the trianion. Possible preconditions under which idealized one-dimensional crystals of (CH)18− and (CH)183− can exhibit superconductivity at finite temperature are considered. © 1998 American Institute of Physics.
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  • 13
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 7637-7644 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibronic (vibrational–electronic) interactions and Jahn–Teller distortions in the mono- and trianions of benzene and [18]annulene, which show delocalized D6h structures in their neutral states, are discussed. E2g modes of vibration remove the orbital degeneracies in these highly symmetric molecules to lead to D2h distortions. We calculate the electronic structures, vibrational modes, and linear vibronic coupling constants of benzene and [18]annulene as well as their deutero-forms using the B3LYP method, a hybrid (Hartree–Fock/density functional theory) method. The C–C stretching E2g mode of 1656 cm−1 and the C–H stretching E2g mode of 3184 cm−1 give large vibronic coupling constants in the mono- and trianions of benzene. On the other hand, in [18]annulene the lowest E2g mode of 116 cm−1 affords extremely large coupling constants in its mono- and trianions to contribute to the Jahn–Teller distortions. The lowest mode of [18]annulene is related to a deformation of the carbon ring of [18]annulene and analogous to acoustic mode of phonon in solid. Thus, the different types of E2g mode play an important role in the Jahn–Teller distortions in negatively charged benzene and [18]annulene. © 1998 American Institute of Physics.
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  • 14
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 10088-10092 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We address the intramolecular vibronic interactions in the C36 tri- and tetra-anions to understand the Jahn–Teller effects and possible superconductivity in "electron-doped" C36 solids. We use the B3LYP hybrid Hartree–Fock/density-functional-theory method for our theoretical analyses. Neither the highest occupied molecular orbital (HOMO) nor the lowest unoccupied molecular orbital (LUMO) of the C36 molecule with D6h symmetry are degenerate, but the next LUMO is twofold degenerate. One can therefore expect Jahn–Teller distortions and interesting electronic properties in the C36 anions. Computed vibronic and electron–phonon coupling constants of the tetra-anion are about twice as large as those of the tri-anion. The second lowest Jahn–Teller active E2g mode of 561 cm−1 is predicted to have the largest coupling constants in both anions. We calculate superconducting transition temperature Tc from McMillan's formula using the coupling constants as well as electronic densities of states at the Fermi level and Coulomb pseudopotentials as parameters. © 1999 American Institute of Physics.
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  • 15
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 11534-11541 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The role of second-order perturbations in the interlayer interactions of gray arsenic is discussed. A hypothetical structural change from the germanium (or diamond) to the arsenic structures is considered using a two-layer model in terms of second-order Jahn–Teller distortions. We show from the concept of transition density or transition force that the second-order term originating from mixing of the pseudodegenerate bands near the Fermi level leads to the well-known layer structure of arsenic. The interesting structure of arsenic is a consequence of orbital interactions near the Fermi level. © 1999 American Institute of Physics.
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  • 16
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 114 (1992), S. 5994-5998 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 17
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 2188-2198 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The role of vibronic interactions in the optical properties of octasilacubane (SiH)8 with Oh symmetry is studied. The lowest optically allowed transition occurs when an electron in the t2u highest occupied molecular orbital (HOMO) is promoted to the t2g lowest unoccupied molecular orbital (LUMO)+2 or an electron in the t2g HOMO−1 is promoted to the t1u LUMO, from the point of view of a one-electron approximation. How the frontier orbitals can couple to the molecular vibrations of (SiH)8 is discussed in detail from density-functional-theory calculations. The vibronic coupling constants of some vibrational modes to the 1T1u electronic excited state that stems from the possible two lowest optically allowed transitions in (SiH)8 are calculated. The low-frequency threefold degenerate T2g mode of 197 cm−1 and the twofold degenerate Eg mode of 403 cm−1 have large vibronic coupling constants, and the vibronic coupling would provide the absorption band at 3.5 eV with approximate energy separations of 25 and 50 meV, respectively, if the optical absorption spectrum is measured in the gas phase or dilute matrix. © 2000 American Institute of Physics.
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  • 18
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 538-545 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Crossing seams between the potential energy surfaces and possible spin inversion processes for the direct conversion of methane to methanol by the bare FeO+ species are discussed by means of the intrinsic reaction coordinate (IRC) approach. There are three crossing seams between the sextet and the quartet potential energy surfaces, and spin inversion should occur twice in the entrance and the exit channels; FeO+(6Σ+)+CH4(1A1)→OFe+(CH4)(6A)→TS1(4A′)→HO–Fe+–CH3(4A)→TS2(4A)→Fe+(CH3OH)(4A)→Fe+(6D)+CH3OH(1A′). The first crossing seam exists in prior to TS1, a four-centered transition state for the cleavage of a C–H bond of methane. This crossing seam is the most important aspect in this reaction pathway because the molecular system should change its spin multiplicity from the sextet state to the quartet state near this crossing region, leading to a significant decrease in the barrier height of TS1 from 31.1 to 22.1 kcal/mol at the B3LYP level of density functional theory. The second crossing seam occurs in the vicinity of the hydroxy intermediate (HO–Fe+–Ch3), but this crossing seam would not play a significant role because the quartet IRC valley always lies below the sextet one in this region of reaction coordinate and accordingly the molecular system would preferentially move on the quartet potential energy surface. The third crossing seam exists in the exit channel in which the elimination of methanol occurs from the product complex. This crossing seam will again lead to spin inversion from the quartet to the sextet state, by which the elimination energy can be decreased from 57.2 to 37.4 kcal/mol in the FeO+/CH4 system. © 1999 American Institute of Physics.
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  • 19
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 249-255 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibronic (vibrational–electronic) interactions and Jahn–Teller distortions in the mono- and trianions and the mono- and trications of coronene are discussed. E2g modes of vibration remove the orbital degeneracies in the highly symmetric D6h molecule to lead to D2h distortions. We calculate and analyze the vibrational modes and the linear vibronic coupling constants of the anions and cations of coronene as well as its deutero-form using the (Becke and Lee, Yang, and Parr) density-functional method. Although there are twelve E2g modes of vibration in coronene, some of them appear to play a significant role in the Jahn–Teller distortions. The lowest frequency mode of 370 cm−1, the C–C stretching mode of 1668 cm−1, and the C–H stretching modes of 3177 and 3193 cm−1 give large coupling constants in the anions. In particular, the 1668 cm−1 mode plays the most important role in the Jahn–Teller distortions both in the anions and cations. There is electron–hole symmetry in the coupling constants in the anions and cations. We also demonstrate an important H/D isotope effect. The highest two C–H stretching modes are important for the Jahn–Teller distortions in coronene; however, the corresponding C–D stretching modes are less important for the Jahn–Teller distortions in deutero-coronene. © 1999 American Institute of Physics.
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  • 20
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 7344-7347 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Orbital–vibronic coupling constants were calculated and analyzed using cluster models with D6h symmetry at the B3LYP level of density functional theory to aid the understanding of the electron–phonon interaction mechanism in magnesium diborate, a new binary superconductor with Tc of 39 K. How the frontier orbitals couple with the E2g modes of molecular vibration in the cluster models is discussed with an emphasis on the symmetry of the relevant molecular orbitals and vibrations. © 2001 American Institute of Physics.
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