Density functional theory spectra

Figure 2 Mid-IR absorption spectra of 1. The experimental spectrum is in CC14 solution. Density functional theory spectra are calculated using the cc-pVTZ basis set and a range of functionals. Band shapes are Lorentzian (y = 4.0 cm-1). Fundamentals are numbered.

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. 

Kesyczynski, J. Goodman, L., Kwiatkowski, J. S., 1997, Density Functional Theory and Post-Hartree-Fock Studies on Molecular Structure and Harmonic Vibrational Spectrum of Formaldehyde , Theor. Chem. Acc., 97, 195. 

Martin, J. M. L., El-Yazal, J., Francois, J.-P, 1996, Structure and Vibrational Spectrum of Some Polycyclic Aromatic Compounds Studied by Density Functional Theory. 1. Naphtalene, Azolene, Phenanthrene, and Anthracene , J. Phys. Chem., 100, 15358. 

Phenylperoxy radical has similarly been a topic of experimental and theoretical interest. Tokmakov et al. " calculated a potential energy surface for phenyl radical and O2 using ab initio G2(MP2) calculations. Weisman and Head-Gordon used time-dependent density functional theory (TD-DFT) calculations to examine the effect of substituents on the phenylperoxy radical s UV-vis absorption spectrum. " Lin and Mebel used ab initio methods to study the phenoxy radical -f O-atom reaction. "... 

The vibrational spectrum of 13 is nicely reproduced by quantum chemical calculations at the CCSD(T) level of theory," whereas density functional theory (DFT) shows a variable performance for 13 depending on the functional employed." This caution holds especially for the distance between the radical... 

The measured electronic structure, occupied or unoccupied, provides the fullest information when also combined with theory. Electronic structure calculations in surface chemistry have advanced immensely in the past decades and have now reached a level of accuracy and predictive power so as to provide a very strong complement to experiment. Indeed, the type of theoretical modeling that will be employed and presented here can be likened to computer experiments, where it can be assumed that spectra can be computed reliably and thus computed spectra for different models of the surface adsorption used to determine which structural model is the most likely. In the present chapter, we will thus consistently use the interplay between experiment and theory in our analysis of the interaction between adsorbate and substrate. Before discussing what quantities are of interest to compute in the analysis of the surface chemical bond, we will briefly discuss and justify our choice of Density Functional Theory (DFT) as approach to spectrum and chemisorption calculations. 

We will of course be rather more focused here. We shall be concerned with the generic computational strategies needed to address the problems of phase behavior. The physical context we shall explore will not extend beyond the structural organization of the elementary phases (liquid, vapor, crystalline) of matter, although the strategies are much more widely applicable than this. We shall have nothing to say about a wide spectrum of techniques (density functional theory [1], integral equation theories [2], anharmonic perturbation... 

Sun, G., Kertesz, M. (2001) Isomer Identification for Fullerene C84 by 13C NMR Spectrum A Density-Functional Theory Study, J Phys Chem A 105, 5212-5220. 

The work of Baerends et al. using density functional theory (DFT) methods confirmed that the energies of the orbitally forbidden or spin-forbidden MLCT transitions are lower than the energies of the metal-centered (MC) transitions (Fig. 3, Table 1) and this placed the MC transitions further up the energy scale in the UV/ Vis absorption spectrum [10-12], The MC (2t7g—>6eg) transitions move to higher energy for the heavier metals of the triad. 

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