Number density, mode coupling theory

The DECP model successfully explained the observed initial phase of the fully symmetric phonons in a number of opaque crystals [24]. The absence of the Eg mode was attributed to an exclusive coupling between the electrons photoexcited near the r point and the fully symmetric phonons. A recent density functional theory (DFT) calculation [23] demonstrated this exclusive coupling as the potential energy surface (Fig. 2.4). The minimum of the potential surface of the excited state shifted significantly along the trigonal (z) axis,... 

A parameterization method of the Hamiltonian for two electronic states which couple via nuclear distortions (vibronic coupling), based on density functional theory (DFT) and Slaters transition state method, is presented and applied to the pseudo-Jahn-Teller coupling problem in molecules with an s2-lone pair. The diagonal and off-diagonal energies of the 2X2 Hamiltonian matrix have been calculated as a function of the symmetry breaking angular distortion modes and r (Td)] of molecules with the coordination number CN = 3... 

Trimerized organic conductors are of special interest, because two electrons per three sites constitute the simplest situation, where both electronic transitions resulting in single- and double-site occupation take place [21]. As one considers larger n-mers, two complications arise. First, the number of equations that should be solved sharply increases. The second complication is the increase in the number of n-meric normal modes, which are coupled to an external electromagnetic field. Recently, Yartsev et al. [22] have proposed using the linear response theory for several variables to describe the optical properties of trimers with arbitrary equilibrium charge density distribution. This approach can be extended to any cluster—the size is limited only by computer facilities. 

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