Hyperfine structure density functional calculations

Eriksson, L. A., Malkina, O. L., Malkin, V. G., Salahub, D. R., 1994, The Hyperfine Structures of Small Radicals from Density Functional Calculations , J. Chem. Phys., 100, 5066. 

The impurity interacts with the band structure of the host crystal, modifying it, and often introducing new levels. An analysis of the band structure provides information about the electronic states of the system. Charge densities, and spin densities in the case of spin-polarized calculations, provide additional insight into the electronic structure of the defect, bonding mechansims, the degree of localization, etc. Spin densities also provide a direct link with quantities measured in EPR or pSR, which probe the interaction between electronic wavefunctions and nuclear spins. First-principles spin-density-functional calculations have recently been shown to yield reliable values for isotropic and anisotropic hyperfine parameters for hydrogen or muonium in Si (Van de Walle, 1990) results will be discussed in Section IV.2. 

Recent calculations of hyperfine parameters using pseudopotential-density-functional theory, when combined with the ability to generate accurate total-energy surfaces, establish this technique as a powerful tool for the study of defects in semiconductors. One area in which theory is not yet able to make accurate predictions is for positions of defect levels in the band structure. Methods that go beyond the one-particle description are available but presently too computationally demanding. Increasing computer power and/or the development of simplified schemes will hopefully... 

Recent Developments in Configuration Interaction and Density Functional Theory Calculations of Radical Hyperfine Structure. 

During the past few years, however, density functional theory (DFT) has become a serious alternative to conventional Hartree-Fock based approaches, also in the area of hyperfine structure calculations. The DFT methods have drastically expanded the size of the systems accessible to theoretical hfs studies. We will in this paper review some recent developments both in the field of ab initio configuration interaction techniques and in the field of density functional theory applied to hfs studies. 

Wetmore et al. have achieved impressive results with the use of Density Functional Theory (DFT) calculations on the primary oxidation and reduction products observed in irradiated single crystals of Thymine [78], Cytosine [79], Guanine [80], and Adenine [81], The theoretical calculations included in these works estimated the spin densities and isotropic and anisotropic hyperfine couplings of numerous free radicals which were compared with the experimental results discussed above. The calculations involve a single point calculation on the optimized structure using triple-zeta plus polarization functions (B3LYP/6-31 lG(2df,p)). In many cases the theoretical and experimental results agree rather well. In a few cases there are discrepancies between the theoretical and experimental results. 

During the last decade, density functional theory (DFT) has evolved into a competitive alternative to conventional ab initio approaches, primarily due to the low computational cost (favorable scaling with number of basis functions). This enables studies of considerably larger systems, with inclusion of electron correlation. In 1993, the first linear combination of Gaussian-type orbital (LCGTO) DFT calculations of radical hyperfine structures appeared in the literature, developed independently by two different research groups. Today a considerable number of DFT studies of radical hyperfine structures is available, and four major review articles summing up the results have appeared. -2i... 

Basis Sets Correlation Consistent Sets Circular Dichro-ism Electronic Complete Active Space Self-consistent Field (CASSCF) Second-order Perturbation Theory (CASPT2) Configuration Interaction Density Functional Applications Density Functional Theory (DFT), Hartree-Fock (HF), and the Self-consistent Field Electronic Diabatic States Definition, Computation, and Applications ESR Hyperfine Calculations Magnetic Circular Dichroism of rt Systems Non-adiabatic Derivative Couplings Relativistic Theory and Applications Structure Determination by Computer-based Spectrum Interpretation Valence Bond Curve Crossing Models. 

Ru(tap)3] and [Ru(tap)2(phen)] with guanosine-5-monophosphate or N-acetyl-tyrosine gives rise to photo-CIDNP signals [125], that is, non-Boltzmann nuclear spin state distributions that has been detected by NMR spectroscopy as enhanced absorption or emission signals. However, the interpretation framework must be confirmed. In order to validate the experimental predictions. Density Functional Theory (DFT) calculations can be performed. These calculations are based on the determination of the electronic structure of the mono-reduced form of Ru(II) complexes in gas phase and aqueous solution. Recently, some of us showed that the electron spin density and the isotropic Fermi contact contribution to the hyperfine interactions with the nuclei agree remarkably well with the observed photo-CIDNP enhancements [34]. Thus, combined photo-CIDNP experiments and DFT calculations open up new important perspectives for the study of polyazaaromatic Ru(II) complexes photoreactions. 

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