Excitation energies and oscillator

The extension of density functional theory (DFT) to the dynamical description of atomic and molecular systems offers an efficient theoretical and computational tool for chemistry and molecular spectroscopy, namely, time-dependent DFT (TDDFT) [7-11]. This tool allows us to simulate the time evolution of electronic systems, so that changes in molecular structure and bonding over time due to applied time-dependent fields can be investigated. Its response variant TDDF(R)T is used to calculate frequency-dependent molecular response properties, such as polarizabilities and hyperpolarizabilities [12-17]. Furthermore, TDDFRT overcomes the well-known difficulties in applying DFT to excited states [18], in the sense that the most important characteristics of excited states, the excitation energies and oscillator strengths, are calculated with TDDFRT [17, 19-26]. 

The TDDFT excitation energies and oscillator strengths calculated for the lowest allowed excited states of MgP [138], ZnP [138, 140], and NiP [137, 138] complexes in their optimized D4h geometry, are reported in Table 15 and compared to CASPT2 [150] and Multireference Moller-Plesset perturbation (MRMP) theory [151] results. 

Table 21 Calculated excitation energies and oscillator strengths (f) for the optically allowed "Ej and Bj and for the dipole forbidden E3 excited states of Zr(P)2, Zr(OEP)2 (in parentheses), Ce(P)2> and Th(P)2 that contribute to the Q, Q, Q", and B bands, compared to the experimental data...

TDDFT methods have also been applied successfully to the description of the linear and nonlinear optical properties of heteroleptic sandwich complexes. The optical spectrum and the hyperpolarizability of Zr(OEP)(OEPz,) for which large first hyperpolarizabilities, /JSHG (SHG=second-harmonic generation) were measured in an electric field induced second-harmonic generation (EFISH) experiment [182], have been investigated by TDDFT methods [134]. The excitation energies and oscillator strengths calculated... 

The same pseudo-spectral expansion has also been applied to the case of two lithium atoms.70 In this, owing to the more complicated nature of Ho, difficulties arise from the finite size of the basis set. The authors use an extrapolation procedure to surmount this difficulty. Because the summation in the second-order energy is dominated by the first term, whose magnitude can be obtained experimentally from the excitation energy and oscillator strength of the corresponding electronic transition, the authors plot the calculated value of Co against the calculated first term for various sizes of basis set, and choose for Co that value which corresponds to the experimental value of the first term. In this way they obtain... 

Fig. 11 Experimental absorption spectra and TDDFT calculated excitation energies and oscillator...

In the present paper, we show that it is possible to calculate both vibrational and electronic transitions of H2SO4 with an accuracy that is useful in atmospheric simulations. We calculate the absorption cross sections from the infrared to the vacuum UV region. In Section 2 we describe the vibrational local mode model used to calculate OH-stretching and SOH-bending vibrational transitions as well as their combinations and overtones [42-44]. This model provides frequencies and intensities of the dominant vibrational transitions from the infrared to the visible region. In Section 3 we present vertical excitation energies and oscillator strengths of the electronic transitions calculated with coupled cluster response theory. These coupled cluster calculations provide us with an accurate estimate of the lowest... 

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