... symmetries and had been proposed by earlier DFT (density functional theory) calculations. From the different hyperareas the supposed charges were integrated in space and processed to electric field gradients (EFG) on M1 and M2 using a point-charge model. The two EFGs were compared with respect to the system...

...R. James Evans; Denis G. Rancourt; Michael Grodzicki Abstract In this first systematic, theoretical study of the complete electric field gradient (EFG) tensor of 57 Fe Mössbauer spectroscopy as a function of chemistry and local structural distortion using electronic structure calculations, local...

... technology and data processing, such as, intense X-ray sources, charge coupled device (CCD) detectors, fast computers, new methodologies and software, it is now possible to determine the electron density distributions in mineral type compounds very accurately, from which the electric field gradient (EFG...

...Bjoern Winkler; Peter Blaha; Karlheinz Schwarz Abstract Ab initio band-structure calculations based on the density functional theory have been performed for forsterite to obtain, with a parameter-free model, electric-field gradients for all nuclei. Calculations based on the generalized gradient...

...R. James Evans; Denis G. Rancourt; Michael Grodzicki Abstract We report ab initio electronic structure calculations that directly relate given local chemical and distortion environments to corresponding hyperfine electric field gradients (EFGs) in 57 Fe Mössbauer spectroscopy, thereby giving...

... angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The size and large distribution of electric field gradients for 35 Cl causes loss of signal in the MAS NMR experiment and this, in combination with the low concentration of Cl and the large chemical shift dispersion, means that even...

... exceeding 30 K, the Mössbauer spectra consist of a somewhat broadened quadrupole doublet with a splitting of 1.73 mm/s at 295 K. From the spectrum recorded at 250 K in an external magnetic field of 60 kOe, it is derived that the sign of the principal component of the electric field gradient (EFG...

... parameters of the electric-field gradient. The signs are all negative and the asymmetry is large (~0.9), implying that an additional distortion is superimposed on the trigonal compression of the polyhedra. The center shifts δ for the two Fe 2+ sites are equal within experimental error limits. From...

..., vibrational spectra, electric field gradients at Al, and Al and F NMR shieldings for AlF 4 − , AlF 5 2 − , AlF 6 3 − , Al ( OH ) 4 − , Al ( OH ) 5 2 − , AlF ( OH ) 3 − , AlF 2 ( OH ) 2 − , AlF 3 ( OH ) 2 2 − , and AlF 2 ( OH ) 3 2 − to assist in determining Al speciation in these glasses. The Al nucleus...

... at 295 K and 4.2 K. The signs of the electric field gradient at M1 and M2 are positive. The average value of the two asymmetry parameters η is 0.20±0.05. The force constants of Fe 2+ at M1 and M2 are 4.7±0.1 eV/Å 2 and 4.2±0.1 eV/Å 2 , respectively. The axial splitting δ is 1120±50 cm -1 for both sites...

.... The electric field gradient at the Fe site and the site distortion are used to propose a model for the site assignment and oxidation mechanism in bannisterite. The results show that two models are compatible with the experimental results of fitting the spectrum of bannisterite. However, the model which allows...

... was obtained for Fe 3+ . For both hedenbergite samples, the Fe 2+ asymmetry parameter η of the electric field gradient (EFG) is quite high, namely 0.7–0.8 regardless of temperature. The orientation of the ferrous magnetic hyperfine field in the EFG principal-axes frame is ~(85° 38°) and is not affected...

..., and 0.27, 0.38, 0.59, 0.89, respectively. The magnitudes of two of the coupling tensors are the greatest found to date in any aluminum compound. Each of the four tensors indicates a strong electronic polarization of the aluminum atoms approximately parallel to b . The external electric field gradient...

... from published X-ray-diffraction data, gives an octahedron-angle variance of 7 and a mean elongation of the octahedron of 1.002. This indicates nearly regular octahedral geometry, and hence a symmetric electric-field gradient around Fe 3+ . A crystal-chemical interpretation for the regular octahedral...

...) MS recorded at 83, 147, 223, and 277 K for HED2, the principal component of the electric field gradient (EFG), V zz , is determined to be positive and the asymmetry parameter 0.70 ≤ η ≤ 0.80. Considering the discrepancy between the calculated and experimental applied-field MS, the obtained results...

... of the full nuclear-interaction hamiltonian. The hyperfine field B hf is found to be collinear to the local principal axis of the electric field gradient (EFG) tensor. The saturation value for B hf is 125.5 kOe. For temperatures below 52 K, the adjusted value for the asymmetry parameter of the EFG is η ≈ 0.8...

... with varying Al:Si and F:OH ratios to investigate the degree of atomic order in zunyite. The quadrupole coupling constant (C Q ) and asymmetry parameter (η) obtained from simulations of 27 Al MAS and MQMAS spectra were compared with those derived from the electric field gradients (EFG), which were calculated...

...-principles calculations of the electric field gradient. The approach presented in this article can be easily applied, not only to clays or aluminosilicate materials, but to any compounds where the NMR parameters of overlapping spectral lines have to be determined. This can also be extended to sites...