The Experts below are selected from a list of 19212 Experts worldwide ranked by ideXlab platform
J H Williams - One of the best experts on this subject based on the ideXlab platform.
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The effect of an Electric Field Gradient on allowed rotational spectra
Journal of Physics B: Atomic Molecular and Optical Physics, 1992Co-Authors: J H WilliamsAbstract:Equations are derived which describe the effect of an Electric Field Gradient on the intensity of allowed rotational transitions. The effect, although small, should be measurable and provides another method for the determination of the sign and magnitude of the molecular Electric quadrupole moment.
Jacques Fraissard - One of the best experts on this subject based on the ideXlab platform.
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Determination of the Electric Field Gradient in RbCaF3 near the phase transition
Solid State Communications, 1992Co-Authors: Mark A. Hepp, Arlette Trokiner, Helene Zanni, Jacques FraissardAbstract:Abstract The fluoroperovskite, RbCaF 3 undergoes a phase transition at 195.5K from a cubic to a tetragonal phase. The order parameter for this transition is directly related to the Electric Field Gradient which arises in the tetragonal phase. In this work, we have used three NMR methods to measure the Electric Field Gradient at the 87 Rb site in a single crystal of RbCaF 3 , very near this transition. These experiments are based on recent theoretical developments which allow the measurement of quadrupole parameters even for nuclei in a weak Electric Field Gradient.
A V Nikolaev - One of the best experts on this subject based on the ideXlab platform.
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ab initio based description of the unusual increase of the Electric Field Gradient with temperature at ti sites in rutile tio 2
Physical Review B, 2020Co-Authors: A V Nikolaev, N M Chtchelkatchev, A V Bibikov, D A Salamatin, A V TsvyashchenkoAbstract:Combining a precise ab initio electron band structure calculation of the ${\mathrm{TiO}}_{2}$ rutile structure with the temperature evolution of the Ti mean-square displacements, we reproduce a puzzling temperature increase of the Electric Field Gradient at Ti sites in ${\mathrm{TiO}}_{2}$, observed experimentally. Our method employs a procedure of averaging two quadrupole electron density components ($L=2$) inside a sphere vibrating with the Ti nucleus at its center, where the key factor introducing the temperature dependence is the square root of the Debye-Waller factor. Although the Debye-Waller factor always reduces the corresponding Fourier component, in ${\mathrm{TiO}}_{2}$ due to the interplay between terms of opposite signs, it results in a net increase of the whole sum with temperature, leading to the growth of the Electric Field Gradient. Quantitatively, we find that the increase of Electric Field Gradient is only half of the experimental value, which we ascribe to anharmonic effects or a strong oxygen position influence. In addition, our method reproduces the unusual temperature dependence of the asymmetry parameter $\ensuremath{\eta}$, which first decreases with temperature, goes to zero, and then increases.
Karen L Sauer - One of the best experts on this subject based on the ideXlab platform.
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density functional theory based Electric Field Gradient database
Scientific Data, 2020Co-Authors: Kamal Choudhary, Jaafar N Ansari, I I Mazin, Karen L SauerAbstract:The deviation of the electron density around the nuclei from spherical symmetry determines the Electric Field Gradient (EFG), which can be measured by various types of spectroscopy. Nuclear Quadrupole Resonance (NQR) is particularly sensitive to the EFG. The EFGs, and by implication NQR frequencies, vary dramatically across materials. Consequently, searching for NQR spectral lines in previously uninvestigated materials represents a major challenge. Calculated EFGs can significantly aid at the search's inception. To facilitate this task, we have applied high-throughput density functional theory calculations to predict EFGs for 15187 materials in the JARVIS-DFT database. This database, which will include EFG as a standard entry, is continuously increasing. Given the large scope of the database, it is impractical to verify each calculation. However, we assess accuracy by singling out cases for which reliable experimental information is readily available and compare them to the calculations. We further present a statistical analysis of the results. The database and tools associated with our work are made publicly available by JARVIS-DFT ( https://www.ctcms.nist.gov/~knc6/JVASP.html ) and NIST-JARVIS API ( http://jarvis.nist.gov/ ).
B Pal - One of the best experts on this subject based on the ideXlab platform.
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Strain Field and Electric Field Gradient for interstitial point defect in simple metals
Journal of research, 2006Co-Authors: J Singh, B PalAbstract:The strain Field and Electric Field Gradient for interstitial proton in simple fee metals are investigated. The proton occupies octahedral site in fee metals. The defect induced charge density used to evaluate valence effect Electric Field Gradient (qv) is calculated self-consistently in the non linear density functional approach using the spherical solid model potential for discrete lattice and Blatt correction for lattice dilation. The elastic continuum model is used to evaluate size effect Electric Field Gradient (qs) considering the dressed point ions interacting through screened Coulomb potential. Both qv and qs are found cylindricaly symmetric at both the first and second nearest neighbours (NNs) yielding the asymmetry parameter (η) to be zero. qs is found dominating over qv by an order of magnitude. The phase shifts are found converging and the scattering is more prominent in Al than in Cu. Both the valence and strain Fields are equally important to explain the Electric Field Gradient (EFG).