Electronic-vibrational coupling mechanism

In the MQC mean-field trajectory scheme introduced above, all nuclear DoF are treated classically while a quantum mechanical description is retained only for the electronic DoF. This separation is used in most implementations of the mean-field trajectory method for electronically nonadiabatic dynamics. Another possibility to separate classical and quantum DoF is to include (in addition to the electronic DoF) some of the nuclear degrees of freedom (e.g., high frequency modes) into the quantum part of the calculation. This way, typically, an improved approximation of the overall dynamics can be obtained—albeit at a higher numerical cost. This idea is the basis of the recently proposed self-consistent hybrid method [201, 202], where the separation between classical and quantum DoF is systematically varied to improve the result for the overall quantum dynamics. For systems in the condensed phase with many nuclear DoF and a relatively smooth distribution of the electronic-vibrational coupling strength (e.g.. Model V), the separation between classical and quanmm can, in fact, be optimized to obtain numerically converged results for the overall quantum dynamics [202, 203]. 

The exciting discovery of super-conductivity in metallic fiillerencs (f) leads us to inquire whether the classic mechanism for superconductivity, namely, effective electron-electron attraction via the interaction of electrons with vibrations of the ions, is applicable here as well. Associated with this is the question of whether the direct electron-electron repulsion in FuUerenes can suppress conventional singlet pairing. In this paper we exploit the special nature of cluster compounds to derive a particularly simple expression for electron-vibrational coupling from which parameters of the superconducting state of fuUerenes are easily calculated. Further, we present arguments why the effective repulsions in fuUerenes are no different than in conventional metals. 

Recently, there has been much interest in the development and application of multidimensional coherent nonlinear femtosecond techniques for the study of electronic and vibrational dynamics of molecules [1], In such experiments more than two laser pulses have been used [2-4] and the combination of laser pulses in the sample creates a nonlinear polarization, which in turn radiates an electric field. The multiple laser pulses create wave packets of molecular states and establish a definite phase relationship (or coherence) between the different states. The laser pulses can create, manipulate and probe this coherence, which is strongly dependent on the molecular structure, coupling mechanisms and the molecular environment, making the technique a potentially powerful method for studies of large molecules. 

The coupling mechanism given above for mixing excited u terms into g electronic terms through vibrational modulation of the ligand field is likely to be less efficient if terms of different spin are involved. In accordance with this, it is observed that spin-forbidden bands are a good deal narrower than are the spin-allowed ones dealt with above, corresponding to reduced overlap of available vibrational structure. Half-widths of a few hundred to one thousand cm-1 seem to be involved. 

A complete quantum mechanical description of electron transfer provides the following expression for the rate with a single, averaged effective internal vibration coupled to the electron transfer [23] ... 

Connection with vibrational lifetime on surfaces. The decay of molecular vibrations in the excitation of the electron-hole pairs of metallic surfaces have been identified with the mechanisms of vibration excitation by tunneling electrons [42]. Intuitively this may seem so. Indeed, an excited vibration may couple to the surface electronic excitations through the same electron-vibration matrix elements of Eqs. (2) and (4). The surface... 

The superconducting ability of [M(dmit)2] complexes, see Fig. 9, has prompted experimental and theoretical vibrational studies of [Ni(dmit)2]z and [Pd(dmit)2]z complexes (z is in the range 0-2—), in order to understand the mechanism of superconductivity in terms of electron-intramolecular and electron-intermolecular vibrational couplings (14, 21). These studies have... 

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