Electronic excitation spectrum

Sukumar, N., and G. A. Segal. 1986. Effect of Aqueous Solvation upon the Electronic Excitation Spectrum of the Glycine Zwitterion A Theoretical Cl Study Using a Fractional Charge Model. J. Am. Chem. Soc. 108, 6880-6884. 

Fio. II. Electron excitation spectrum of 1,1-diphenylethyIene in concentrated H2SO4 according to Gold and Tye (1962a). 

In recent years, the first applications of DFT to excited electronic states of molecules have been reported. In the so-called time-dependent DFT (TDDFT) method, the excitation energies are obtained as the poles of the frequency-dependent polarizability tensor [29], Several applications of TDDFT with standard exchange correlation functionals have shown that this method can provide a qualitatively correct description of the electronic excitation spectrum, although errors of the order of 0.5 eV have to be expected for the vertical excitation energies. TDDFT generally fails for electronic states with pronounced charge transfer character. 

Qualitatively new results concerning the determination of the neutrino rest mass were obtained in 1980, when the data reduction of a set of experiments performed for more than 5 years at the Moscow Institute of Theoretical and Experimental Physics (ITEP) (Lubimov et al, 1980, 1981) for the first time give the lower limit on the neutrino rest mass. The /J-electron source was a doubly tritrated amino acid, valine (C5HnN02). The early reductions of the results obtained in these experiments have shown that the confidence interval for the neutrino mass substantially depends on the chosen theoretical model. Since the real electron excitation spectrum of the / source was not known, the experimental data were reduced for two model cases ... 

If we substitute a> = () into the above, we arrive at a frequency-independent kernel expression, which can be derived by differentiating Eq. (2-67) with respect to the electron density [110]. With the frequency-independent kernel, one can obtain a one-electron excitation spectrum from TDOEP [110]. The frequency-dependent kernel offers a unique opportunity to quantity the impact of the adiabatic approximation [114]. 

Gwaltney SR, Bartlett RJ (1998) Coupled-cluster calculations of the electronic excitation spectrum of free base porphin in a polarized basis. J Chem Phys 108 6790-6798. 

The response function x so obtained includes new effects introduced in the electron excitation spectrum by the ion-induced rearrangement of charge. 

These effects have actually also been observed here in the photoionization and electronic excitation spectrum of HCN and FCN (Tables 16 and 28, respectively). Thus the first IP in both molecules is out of a 71 MO and hardly changes from 13.61 eV to 13.65 eV when F replaces H. On the other hand, the first g MO (non-bonding on nitrogen) ionization energy goes from 14.00 eV in HCN to 14.56 in FCN The calculated spectra at the... 

All of the physical measurments point to the equivalence of all the platinum atoms (in a noninteger oxidation state) in a chain. The results of the numerous measurements on K2Pt(CN)4Bro.3(H20)s, demonstrates this system to be a one-dimensional metal undergoing a metal-insulator transition as the temperature is lowered. The far infrared and optical measurements show that the electronic excitation spectrum is not that of a simple one-dimensional metal but has a complex behavior at low frequencies. The available data from many diverse types of experiments have been analyzed in terms of numerous models. This system is currently best characterized in terms of a one-dimensional metal undergoing a Peierls transition to a semiconductor at low temperatures, with evidence for the presence of a pinned charge density wave. Further careful measurements of the partially oxidized tetracyanoplatinates are necessary to fully understand the applicability of various one-dimensional models to this class of materials. 

A theoretical description of electron-phonon coupling effects in unstable-moment compounds demands a thorough understanding of their electronic excitation spectrum. It has already been qualitatively described in the introduction. In this section we give a firmer theoretical foundation to these concepts for the 4f impurity case as well as the periodic lattice of 4f ions in a metalUc compound. For the Ce or Yb systems the physics for these two cases is adequately described by the (degenerate) Anderson and Anderson lattice Hamiltonians respectively. For a single impurity it reads n = flfj... 

Characteristic differences arise in the electronic excitation spectrum of heavy-fermion magnets in the different regimes. For a magnetic state with well localized moments and only moderate enhancement of y (i.e., of order 0.1 J mol ) as in CeAlj, the following picture has been proposed (Doniach 1977, Nozieres 1985) starting from band electrons and ionic f-states, the quasiparticle renormalizations stop when spin order of somewhat renormalized moments occurs. The corresponding RKKY interactions with energy scale are mediated by... 

Alexander, M.H., Walton, A.R., Yang, M., Yang, X., Hwang, E., Dagdigian, P.J. A collaborative theoretical and experimental study of the structure and electronic excitation spectrum of the BAr and BAr2 complexes, J. Chem. Phys. 105 (1997) 6320-6331. 

Thus far we have focused on anomalous lanthanide and U-compounds that are metallic in the sense that their resistivity at low temperatures approaches that of normal metals and dptdT is positive for T > 0. There is another interesting class of anomalous 4f and 5f compounds that display a small, typically 10-100 K, semiconducting gap in their low-temperature electronic excitation spectrum. Classic examples of this behavior are SmBe (Allen et al. 1979) and YbBi2 (Kasaya et al. 1985). Recently, several new Ce and U compounds have been discovered that appear to belong to this class and that have revitalized interest in these types of materials. (See Aeppli and Fisk (1992) for a brief review and discussion of these systems at ambient pressure.) A central question raised here is to what extent the physics of these semiconductors is related to that in anomalous metallic compounds, particularly as revealed from high pressure measurements. 

A third major innovation in polymer physics during the past decade is the recognition that because they are quasi-one-dimen-sional materials, some polymers exhibit collective semiconducting ground states(5,8). In contrast to the pervasive effects of disorder in almost all polymers, however, the occurrence of collective phenomena is uncommon. Specifically, it is characteristic of macromolecules like polyacetylene which have experienced a symmetry-lowering structural modification that introduces a semiconductor gap into what would have been a metallic electronic excitation spectrum. Moreover, in such materials the consequences of disorder can be dramatically different from those noted in the previous lecture. Thus, in this third and final lecture we examine the destruction of the collective semiconducting ( Peierls ) ground state in doped polyacetylene by the interaction of the conduction electrons with a disordered array of donors or acceptors. 

While the classical models can reproduce and sometimes predict some structural properties, they are unable to inform about the electronic characteristics of insulators, because they assume that the electrons are frozen around the ionic cores. The next step consists in finding the microscopic origin of the forbidden gap present in the electronic excitation spectrum, which is the defining property of the insulating state. 

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