Electronic spectra, calculations

Ifse the electronic Spectrum dialog box to display and analyze the IfV-vis spectrum produced by a singly excitetl Cl calculation. This dialog box is available only after yon do a single point Cl semi-einpirical calculation. Electronic Spectrum is then activated on the Compute menu. 

The longest wavelength absorption transition for ethene calculated by HyperChem using PM3 is 207 nm, which compares favorably with the experimental value of 190-200 nm. After you compute an electronic spectrum with HyperChem, you can use the table below to assign computed transitions and qualitatively assess the accuracy of the computation. ... 

Indazoles have been subjected to certain theoretical calculations. Kamiya (70BCJ3344) has used the semiempirical Pariser-Parr-Pople method with configuration interaction for calculation of the electronic spectrum, ionization energy, tt-electron distribution and total 7T-energy of indazole (36) and isoindazole (37). The tt-densities and bond orders are collected in Figure 5 the molecular diagrams for the lowest (77,77 ) singlet and (77,77 ) triplet states have also been calculated they show that the isomerization (36) -> (37) is easier in the excited state. 

It is clear that an ah initio calculation of the ground state of AF Cr, based on actual experimental data on the magnetic structure, would be at the moment absolutely unfeasible. That is why most calculations are performed for a vector Q = 2ir/a (1,0,0). In this case Cr has a CsCl unit cell. The local magnetic moments at different atoms are equal in magnitude but opposite in direction. Such an approach is used, in particular, in papers [2, 3, 4], in which the electronic structure of Cr is calculated within the framework of spin density functional theory. Our paper [6] is devoted to the study of the influence of relativistic effects on the electronic structure of chromium. The results of calculations demonstrate that the relativistic effects completely change the structure of the Or electron spectrum, which leads to its anisotropy for the directions being identical in the non-relativistic approach. 

H = di(Z—iy di are the potential parameters I is the orbital quantum number 3 characterizes the spin direction Z is the nuclear charge). Our experience has show / that such a model potential is convenient to use for calculating physical characteristics of metals with a well know electronic structure. In this case, by fitting the parameters di, one reconstructs the electron spectrum estimated ab initio with is used for further calculations. 

The results of calculations for the points F—27r/a(0, 0,0) and A —27r/a(0,0.5,0) of the Brillouin zone are listed in Table 1. It can be seen that the energy eigenvsdues differ, on the average, by S Q Ryd between the two csdculations. Such an accuracy is quite sufficient for most applications. The qualitative picture of the electron spectrum is in complete agreement with our previous SPRKKR calculation. 

The extensive calculations of Serrano-Andres et al [31] have shown a spurious valence-Rydberg mixing in the CASSCF wave functions when valence (7t,7r )and Rydberg orbitals are optimized all together in a state average calculation it was shown that these orbitals loose their diffuse character and instead tend to provide an extra correlation to valence orbitals. To avoid such interaction, the orbitals used for the Cl treatment of the electronic spectrum were obtained by a two step procedure ... 

Although low energy structures for prephenate have been reported before [40], these have been optimized using gas-phase quantum mechanics, and are not compatible with the structure determined for the prephenate inside the active site of CM [41], The first calculation of the electronic spectrum of prephenate inside the active site of the enzyme was done by our group [18]. Using the MD/QM method described, we were also able to obtain an electronic spectrum for prephenate in solution. 

The structure and IR spectrum of furazan were studied by vibrational S CF (VSCF) and Cl (VCI) calculations based on a high-quality potential derived from electronic structure calculations up to the CCSD(T)/aug-cc-pCVQZ level. Excellent agreement was found between the computed and the experimental results <2005THA327>. 

McMahon et al. contributed to this field not only by revealing the electronic spectrum of S-37111 but also by elucidating — on the basis of studies with labeled compounds — the complex mechanism of the automerizations and isomerizations of the three C3H2 species S-2, T-36 and S-37.69,112 A complete record, including high level calculations, was published by McMahon.69... 

Fig. 8.8. Experiment set-up and obtained results. Counter-clockwise, from top left schematic view of the set-up for the activation experiment, accelerated electron spectrum as measured by a magnetic spectrometer, full differential cross section for the reaction 197Au(7, n)196Au (dotted) and bremsstrahlung spectrum reconstructed after the deconvolution calculations (solid), x-ray emission spectrum of 196Au measured after the gold sample irradiation...

The CASSCF/CASPT2 calculations were performed with an active space including the five nd, the (n + l)s, the three (n+ l)p orbitals, and a second set of nd orbitals to account for the double shell effect. The importance of including a second 3d shell in the active space was detected in an early study of the electronic spectrum of the nickel atom [2]. This had already been suggested from MRCI results [1]. The results obtained by RT at about the same time indicated that such effects are effectively accounted for when a method is used that includes cluster corrections to all orders, like the QCI method used by them [3]. This result will hold true also for the less approximate coupled cluster method CCSD(T). 

Until recently, only estimates of the Hartree-Fock limit were available for molecular systems. Now, finite difference [16-24] and finite element [25-28] calculations can yield Hartree-Fock energies for diatomic molecules to at least the 1 ghartree level of accuracy and, furthermore, the ubiquitous finite basis set approach can be developed so as to approach this level of accuracy [29,30] whilst also supporting a representation of the whole one-electron spectrum which is an essential ingredient of subsequent correlation treatments. 

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