Perturbation dielectric function, effective

X. Gonze, D.C. Allan and M.P. Teter, "Dielectric tensor, effective charges and phonons in a-quartz by variational density-functional perturbation theory," Phys. Rev. Lett. 68 (1992), 3603-3606. 

Equation 23 can be significantly simplified in the limit of dilute media, that is, for low metal concentrations, since in this case the local field factor is the same for all inclusions and is given by Eq. (4). D. Ricard et al. have proposed a straightforward perturbation method to get the expression of x e// iii dilute medium approximation [79]. The optical Kerr effect in the material amounts to modifying the effective dielectric function under the action of the applied field Eq as... 

The response of a crystal to an external electric field E is described in terms of the conductivity a through the relation J = induced current (for details see Appendix A). Thus, the conductivity is the appropriate response function which relates the intrinsic properties of the solid to the effect of the external perturbation that the electromagnetic field represents. The conductivity is actually inferred from experimental measurements of the dielectric function. Accordingly, our first task is to establish the relationship between these two quantities. Before we do this, we discuss briefly how the dielectric function is measured experimentally. 

As a consequence of the local nature of V (x) the TDLDA possesses several desirable qualities not available in the usual RPAE. From a purely practical point of view, the differential equations approach permits all the excited orbitals (bound and continuum) to be automatically included through the Green function regardless of the size of the atom. In the language of perturbation theory, one easily sums all the dipolar particle-hole channels which couple the atomic shells. More Importantly however, the effective field, (x o)), depends explicitly on space and frequency which allows a pictorial representation of atomic dynamics. In particular, one can define an effective local dielectric function,... 

The MFA [1] introduces the perturbation due to the solvent effect in an averaged way. Specifically, the quantity that is introduced into the solute molecular Hamiltonian is the averaged value of the potential generated by the solvent in the volume occupied by the solute. In the past, this approximation has mainly been used with very simplified descriptions of the solvent, such as those provided by the dielectric continuum [2] or Langevin dipole models [3], A more detailed description of the solvent has been used by Ten-no et al. [4], who describe the solvent through atom-atom radial distribution functions obtained via an extended version of the interaction site method. Less attention has been paid, however, to the use of the MFA in conjunction with simulation calculations of liquids, although its theoretical bases are well known [5]. In this respect, we would refer to the papers of Sese and co-workers [6], where the solvent radial distribution functions obtained from MD [7] calculations and its perturbation are introduced a posteriori into the molecular Hamiltonian. 

X. Gonze and C. Lee, "Dynamical matrices, Bom effective charges, dielectric permittivity tensors, and interatomic force constants from density-functional perturbation theory," Phys. Rev. B 55 (1997), 10355-10368. 

Fig. 15 Sensitivity of the real propagation constant (—) and effective index (---) of a surface plasmon on a metal-dielectric interface to a bulk refractive index change as a function of wavelength calculated rigorously from eigenvalue equation and using the perturbation theory. Waveguiding structure gold-dielectric (nj = 1.32)...

The IR spectra of Chi a monolayers are much more complicated than those of the multilayer, owing to a nonintegrating effect of the monolayer, which reveals the perturbing effect of the different dielectric environment on each functional group. To understand the influence of... 

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