Value Of Electric Field Gradient Research Articles

Nuclear spin alignment of sodium ions via electric field gradients in phospholipid membranes.

The electric field gradient (EFG) has the potential to control both the direction and energy levels of nuclear spins greater than 1/2, a phenomenon known as nuclear electric resonance. Sodium ions on phospholipid membranes, having a nuclear spin of 3/2, can be influenced by surrounding EFGs. Driven by the complex behavior of anisotropic rotation and diffusion of phospholipid molecules, we conducted theoretical investigations and molecular dynamics simulations to study the characteristics of the EFG in this unique environment. Our results demonstrate a tendency for the principal axis of the maximum component of the effective EFG to align orthogonally to the membrane at the position of sodium ions coordinated with phospholipids. This alignment provides a unified precession axis for the nuclear spins of sodium ions, which potentially leads to a consistent definition of quantum information across the membrane. The values of the effective EFG's maximum component suggest energy level gaps of the nuclear spins in the range of tens of kHz, frequencies that have been identified in nerve electromagnetic waves. Consequently, such coherent directionality and energy levels may influence nearby proton and phosphorus nuclear spins, opening the possibility of constructing biological quantum computing systems based on membrane-associated spin interactions and evolutions.

Cd implantation in α−MoO3 : An atomic scale study

Lamellar $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{MoO}}_{3}$ crystals were implanted with low fluence of radioactive $^{111\mathrm{m}}\mathrm{Cd}$ ions at ISOLDE-CERN. Subsequently, we have probed the interaction of the Cd impurity in the lattice with native point defects, such as oxygen vacancies, as a function of annealing temperature using the time differential perturbed angular correlations nanoscopic technique. The experimental data were complemented and interpreted by modeling different Cd-defect configurations in $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{MoO}}_{3}$ with first-principles density functional theory (DFT). The agreement between experiments and DFT simulations shows that only the interstitial Cd (${\mathrm{Cd}}_{I}$) prevails in the van der Waals gap, by inducing a polaron effect. Upon raising the annealing temperature, ${\mathrm{Cd}}_{I}$ is able to trap hole charge carriers resultant from the oxygen vacancies ${V}_{\mathrm{O}}$. Oxygen vacancies were found to form most commonly at two-fold coordinated (O2) atoms. According to comparison DFT results with the experimental electric field gradient values (${V}_{zz}$ and $\ensuremath{\eta}$) and the calculated formation energies for different defect complexes, the configuration of ${\mathrm{Cd}}_{I}$ with two (O2) vacancies (${V}_{\mathrm{O}2}$), located at different planes, is found to be more favorable and stable than the other defect configurations. The electron-polaron formation around the Cd impurity at an interstitial site is enhanced by inducing (O2) vacancies with the creation of hole polaron states.

High order relativistic corrections on the electric field gradient within the LRESC formalism.

In this work, we present relativistic corrections to the electric field gradient (EFG) given by the Linear Response Elimination of the Small Component (LRESC) scheme at 1/c2 order and including for the first time spin-dependent (SD) corrections at 1/c4 order. We show that these new terms improve the performance of LRESC as results with this methodology are very close to those calculated at the four-component Dirac-Hartree-Fock (4c-DHF) level. We assess the new corrections in BrY and AtY di-halogen (Y = F, Cl, Br, I, and At) and XZY bi-linear molecules (Z = Zn, Cd, and Hg; X, Y = F, Cl, Br, I, and At). At the 4c-DHF level, we analyze the contributions coming from the large and small components of the relativistic 4c wave function to the electronic part of EFG and compare them with the LRESC corrections to find their electronic origin. For the HgX2 (X = Cl, Br, and I) subset, when the SDcorrecting terms are included, LRESC calculations match very well with 4c-DHF ones and those from the literature, with differences less than 1% for molecules containing up to three heavy atoms. We show that LRESC gives accurate values of EFG, allowing the analysis of the electronic origin of relativistic effects in terms of well-known nonrelativistic operators.

Crystallographic and Computational Characterisation of the Potential PET Tracer 1,4,7‐Triazacyclononane‐1,4,7‐tri(methylenephosphonato)gallium(III)

AbstractThe macrocyclic chelator 1,4,7‐triazacyclononane‐1,4,7‐tri(methylenephosphonic acid) (H6NOTP) has shown significant promise for use in positron emission tomography with the positron‐emitting radionuclide 68Ga3+. We report the X‐ray crystal structure of the neutral complex 1,4,7‐triazacyclononane‐1,4,7‐tri(methylenephosphonato)gallium(III) ([Ga(H3NOTP)]), which crystallised in the centrosymmetric space group P21/n. The coordination geometry of the Ga3+ ion is distorted octahedral with three macrocyclic amine N donor atoms and three singly deprotonated phosphonato O donor atoms. Two discrete enantiomers, Δ(λλλ)‐SSS and Λ(δδδ)‐RRR, are present as a racemate within the unit cell. Intermolecular hydrogen bonds between phosphonic acid groups of adjacent complexes form a two‐dimensional sheet network. Density functional theory (DFT) calculations supported the observation of complexes with low electric field gradient values with slight but significant deviations from ideal octahedral geometry. The DFT calculations were also used to investigate the influence of intermolecular interactions and ligand protonation states on the coordination environment and surface charge distribution.

Relativistic Fock space coupled-cluster study of bismuth electronic structure to extract the Bi nuclear quadrupole moment

We report the value of the electric quadrupole moment of $^{209}$Bi extracted from the atomic data. For this, we performed electronic structure calculations for the ground $^4S^o_{3/2}$ and excited $^2P^o_{3/2}$ states of atomic Bi using the Dirac-Coulomb-Breit Hamiltonian and the Fock space coupled cluster method with single, double, and full triple amplitudes for the three-particle Fock space sector. The value of the quadrupole moment of $^{209}$Bi, $Q(^{209}$Bi$)=-418(6)$~mb, derived from the resulting electric field gradient values and available atomic hyperfine splittings is in excellent agreement with molecular data. Due to the availability of the hyperfine constants for unstable isotopes of Bi, current atomic calculation allows also to correct their quadrupole moments.

Locally symmetric oxygen vacancy around Cd impurities in CeO2

A detailed investigation of the electronic structure in the neighborhood of Cd impurities in ${\mathrm{CeO}}_{2}$ has been performed by ab initio calculations to elucidate the interplay between the oxygen vacancies and electric quadrupole interactions. The quadrupole frequency related to the major component of the electric-field gradient (EFG) at impurities sites from its neighboring charge density as well as its symmetry were calculated by simulating oxygen vacancies at oxygen nearest neighbor of Cd. Results show a very good agreement with experimental hyperfine interactions measurements at the $^{111}\mathrm{Cd}$ nucleus replacing Ce at ${\mathrm{CeO}}_{2}$. A systematic mapping of oxygen vacancies in ${\mathrm{CeO}}_{2}$ supercells was proposed within the framework of density-functional theory using the wien2k code focusing on the electronic distribution in the vicinity of Cd impurities. Results show that the calculated values of EFG crucially depend on impurity-vacancy complex position and the striking axial symmetry observed when an oxygen monovancy is at the nearest neighborhood of Cd is explained by a rearrangement of its $p$ orbitals.

Multiferroic bismuth ferrite: Perturbed angular correlation studies on its ferroic α−β phase transition

Work of numerous research groups has shown different outcomes of studies of the transition from the ferroelectric $\ensuremath{\alpha}$-phase to the high temperature $\ensuremath{\beta}$-phase of the multiferroic, magnetoelectric perovskite Bismuth Ferrite (${\mathrm{BiFeO}}_{3}$ or BFO). Using the perturbed angular correlation (PAC) method with $^{111m}\mathrm{Cd}$ as the probe nucleus, the $\ensuremath{\alpha}$ to $\ensuremath{\beta}$ phase transition was characterized. The phase transition temperature, the change of the crystal structure, and its parameters were supervised with measurements at different temperatures using a six detector PAC setup to observe the $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ decay of the $^{111m}\mathrm{Cd}$ probe nucleus. The temperature dependence of the hyperfine parameters shows a change in coordination of the probe ion, which substitutes for the bismuth site, forecasting the phase transition to $\ensuremath{\beta}$-BFO by either increasing disorder or formation of a polytype transition structure. A visible drop of the quadrupole frequency ${\ensuremath{\omega}}_{0}$ at a temperature of about ${T}_{c}\ensuremath{\approx}{820}^{\ensuremath{\circ}}\phantom{\rule{0.16em}{0ex}}\mathrm{C}$ indicates the $\ensuremath{\alpha}\ensuremath{-}\ensuremath{\beta}$ phase transition. For a given crystal symmetry, the DFT-calculations yield a specific local symmetry and electric field gradient value of the probe ion. The $Pbnm$ ($\ensuremath{\beta}$-BFO) crystal symmetry yields calculated local electric field gradients, which very well match our experimental results. The assumption of other crystal symmetries results in significantly different computed local environments not corresponding to the experiment.

105Pd NMR and NQR study of the cubic heavy fermion system Ce3Pd20Si6

We report 105Pd nuclear magnetic resonance (NMR) and nuclear quadrupolar resonance (NQR) measurements on a single crystal of Ce3Pd20Si6, where antiferroquadrupolar and antiferromagnetic orders develop at low temperature. From the analysis of NQR and NMR spectra, we have determined the electric field gradient (EFG) tensors and the anisotropic Knight shift (K) components for both inequivalent Pd sites—Pd(32f) and Pd(48h). The observed EFG values are in excellent agreement with our state-of-the-art density functional theory calculations. The principal values of the quadrupolar coupling are MHz and MHz, for the Pd(32f) and Pd(48h) sites, respectively, which is large compared to the Larmor frequency defined by the gyromagnetic constant MHz/T for 105Pd. Therefore, the complete knowledge of K and the EFG tensors is crucial to establish the correspondence between NMR spectra and crystallographic sites, which is needed for a complete analysis of the magnetic structure, static spin susceptibility, and the spin-lattice relaxation rate data and a better understanding of the groundstate of Ce3Pd20Si6.

Monitoring LaMnO3 Jahn–Teller distortion via electric-field gradient ab initio calculations

The electric field gradient (EFG) is studied via ab initio density functional theory calculations for the prototype LaMnO3 manganite under ferromagnetic and A-type antiferromagnetic configurations with different values of on-site Hubbard U potential correction on the Mn-3d states. It is shown that the relaxation of internal atomic positions inhibits fully activated MnO6 Jahn–Teller distortions, as determined by calculating the EFG tensor and the Jahn–Teller distortion parameter Δ. In fact, a strong correlation between the EFG values, especially at the La site, and the Jahn–Teller distortion was found and used to confirm the importance of an appropriate description of the electron–electron correlations when predicting the ground state properties of LaMnO3 using a GGA + U approximation for the exchange-correlation functional.

The Predictive Power of Different Projector-Augmented Wave Potentials for Nuclear Quadrupole Resonance

The projector-augmented wave (PAW) method is used to calculate electric field gradients (EFG) for various PAW potentials. A variety of crystals containing reactive nonmetal, simple metal, and transition elements, are evaluated in order to determine the predictive ability of the PAW method for the determination of nuclear quadrupole resonance frequencies in previously unstudied materials and their polymorphs. All results were compared to experimental results and, where possible, to previous density functional theory (DFT) calculations. The EFG at the 14N site of NaNO2 is calculated by DFT for the first time. The reactive nonmetal elements were not very sensitive to the variation in PAW potentials, and calculations were quite close to experimental values. For the other elements, the various PAW potentials led to a clear spread in EFG values, with no one universal potential emerging. Within the spread, there was agreement with other ab initio models.

Theoretical studies of cubic AuCu3-type intermetallic actinide compounds NpPx3 (Px=Al, Ga, In)

In this paper, we explore the structural, magnetic, electronic specific heat, electric field gradient (EFG) as well as quadrupole coupling constant of NpPx3 (Px = Al, Ga, In) by using LDA, GGA, GGA + U and HF-PBEsol. The relativistic effects of electrons of the actinides are considered by spin-orbit coupling calculations. The comparison of the calculated structural parameters, magnetic moments and EFG of these materials satisfy the available experimental results. This consistency shows the effectiveness of our theoretical tools. The calculated EFG and quadrupole coupling constant value increase in NpPx3 from Al to In due to change of fermions. The EFG and quadrupole coupling constant in NpPx3 (Px = Al, Ga, In) is mainly originated from f-f and p-p contributions of Np atom and p-p contribution of Al, Ga and In atom.

Electric field gradient analysis of RIn3 and RSn3 compounds (R = La, Ce, Pr and Nd)

In this paper we explore the electronic charge distribution at different atomic sites in the rare-earth intermetallics RIn3 and RSn3 (R = La, Ce, Pr and Nd) using the analysis of the electric field gradients (EFGs) calculated by the FP-LAPW + lo method. The f-state in these compounds makes them strongly correlated systems, therefore the exchange and correlations are treated with GGA + U along with the GGA whereas GGA + SOC is also used to treat the relativistic effects. The calculated EFG values are consistent with the experimental results of the Mössbauer spectroscopy for LaSn3, CeSn3, CeIn3, PrSn3 and NdSn3 and therefore we expect that our calculated values for the remaining compounds will be also consistent with the experimental results. The anisotropy of the charge distribution in the vicinity of a nucleus causes EFG and therefore the orbitals contribution of EFG i.e., Vzzp−p, Vzzs−d, Vzzd−d, Vzzp−f and Vzzf−f are evaluated for nonmagnetic and AMF phases using GGA, GGA + U and GGA + SOC.

A comparative study of troilite in bulk ordinary chondrites Farmington L5, Tsarev L5 and Chelyabinsk LL5 using Mössbauer spectroscopy with a high velocity resolution

A comparative study of troilite in bulk ordinary chondrites Farmington L5, Tsarev L5 and Chelyabinsk LL5 was carried out using Mössbauer spectroscopy with a high velocity resolution and two different fitting programs: in the first case the quadrupole interaction was treated as a perturbation to the first order on the nuclear Zeeman levels, whereas in the other case the full static Hamiltonian of the hyperfine interaction (magnetic+quadrupole) was taken into account for the excited and ground nuclear states. The first fit of the Mössbauer spectra revealed a difference between the hyperfine magnetic field values as found for troilite in Farmington L5 (307.7±0.2kOe) and in both Tsarev L5 (311.3±0.3kOe) and Chelyabinsk LL5 (311.9±0.5kOe), although the spectral component of troilite could not be fitted satisfactorily. In contrast, the second fit resulted in a more accurate description of the troilite spectral component, and revealed a difference in the electric field gradient values found for troilite in Farmington L5 (−4.85±0.03×1021V/m2) and in both Tsarev L5 (−4.68±0.05×1021V/m2) and Chelyabinsk LL5 (−4.66±0.04×1021V/m2), while the difference between the hyperfine magnetic field values was less pronounced.

Electric quadrupole and magnetic dipole interactions at 181Ta impurity in Zr2Ni7 intermetallic compound: Experiment and first-principles calculations

Electric quadrupole interactions at 181Ta impurity in the intermetallic compound Zr2Ni7 have been studied by perturbed angular correlation technique. It has been found that there are two electric field gradients (EFG) at the 181Ta site due to two different crystalline configurations in Zr2Ni7, while contradictory results were reported from previous investigations. The values of EFG at room temperature have been found to be Vzz=7.9×1017V/cm2 and 7.1×1017V/cm2 corresponding to present experimental values of quadrupole frequencies and asymmetry parameters for the two sites: ωQ1=70.7(1)Mrad/s, η=0.28(1), δ=0.8(2)% (site fraction 84%) and ωQ2=63(1)Mrad/s, η=0.35(5), δ∼0 (site fraction 9%). Electric field gradients and asymmetry parameters have been computed from the complementary first-principles density functional theory (DFT) to compare with present experimental results. Our calculated values of EFG are found to be in close agreement with the experimental results. No magnetic interactions in Zr2Ni7 have been observed at 298 and 77K which implies that there is no ferromagnetic ordering in this material down to 77K. This observation is corroborated by theoretical calculations, wherein no magnetic moment or hyperfine field is found at any atomic site.

Density functional theory study of nitrogen-14 nuclear quadrupole coupling parameters of L-histidine: hydrogen-bonded system

The calculations of nitrogen-14 nuclear quadrupole parameters, nuclear quadrupole coupling constant, χ, and asymmetry parameter, η, of L-His were done in two distinct environments: one as a free fully optimized molecule, an isolated molecule with the geometrical parameters taken from X-ray, and the other in the orthorhombic and monoclinic solid states. The most probable interacting molecules with the central molecule in the crystalline phase were considered in the hexameric clusters to include hydrogen-bonding effects in the calculations. The computations were performed with PW91P86/6-31++G** and B3LYP6-31++G** methods using the Gaussian 98 program. The good agreement between the nitrogen-14 quadrupole parameters of the free His and imidazole molecules with their microwave available data demonstrates that the applied level of theory and the 6-31++G** basis set are suitable to obtain reliable electric field gradient values. In the solid state, the shifts of quadrupole coupling parameters from the monomer to the solid phase are reasonably well reproduced for the amino and imino sites of imidazole ring in a hexameric cluster. That implies the fact that the hexameric cluster worked effectively to generate the results which are compatible with the experiment. The quadrupole coupling constant values of -N(+) H(3) group are in fair agreement with the experiment. This discrepancy is due to the absences of vibrational effects and the rotation of -N(+) H(3) group around N-C(α) bond.

Electric field gradient calculations in ZnO samples implanted with 111In(111Cd)

A first-principles study of the electric field gradient (EFG) calculated for ideal and 111In(111Cd) implanted ZnO samples is reported in the present work. The study was made for ZnO ideal hexagonal structures and supercells were introduced in order to consider the possible implantation environments. The calculation was done using the “WIEN2k” code within the density functional theory, the exchange and correlation effects were determined by the GGA approximation. Three possible 111In(111Cd) implantation configurations were studied, one substitutional incorporation at cation site and two interstitials. The obtained EFG values for the ideal structure and the substitutional site are in good agreement with the experimental reports measured by perturbed angular correlation (PAC) and high precision nuclear magnetic resonance (NMR). Thus, the ascription of substitutional incorporation of 111In(111Cd) probe atom at the ZnO cation site after annealing was confirmed.

NMR study of the electric field gradient in the paramagnetic phase of M3V2O8 (M = Co, Ni) compounds

The NMR spectra and the decay of a spin echo signal from 51V nuclei in Kagome-staircase Co3V2O8 (CVO) and Ni3V2O8 (NVO) single crystals are measured in the temperature range 30–300 K and a magnetic field H0 = 20 kOe. The orientation dependences of the 51V NMR line shape are used to determine the electric field gradient (EFG) parameters, namely, quadrupole frequency νQ and asymmetry parameter η. These parameters for NVO and CVO are νQ = 180(10) kHz, η = 0.5(1) and νQ = 130(10) kHz, η = 0.6(1), respectively. A comparison of the results of calculating EFG tensors with a point charge model and the NMR data indicates that the crystallographically equivalent vanadium atoms in the Ni3V2O8 and Co3V2O8 compounds differ in the EFG axis orientation. M3V2O8 crystals are found to have vanadium positions (V1, V2) with different orientations of the z axis, which specifies the direction of the principal value of EFG (Vzz): these orientations lie in the bc plane and make an angle of either +51(5)° (V1) or −51(5)° (V2) with axis c. In the temperature range 30–300 K, the EFG tensor components and the local symmetry of the charge surrounding of the vanadium positions in NVO and CVO oxides are found to change insignificantly.

Effect of Noncollinear Magnetic Order on the Hyperfine Interactions in Pt3Fe

The investigations of the hyperfine interactions in Pt3Fe with the noncollinear magnetic order by means of ab initio methods are presented. It is shown that the ground state magnetic order of Pt3Fe is of noncollinear character. Electric field gradient and hyperfine magnetic field at 57 Fe nucleus were calculated and their dependence on the strength of Coulomb correlation interaction is discussed. The calculated values of electric field gradient correspond with the experimental data and the best agreement was found when the enhanced Coulomb correlation interaction for 3d-states of Fe was considered. Lattice, local valence electron (3d, 4p) and weakly bound 3p semicore electron contributions to electric field gradient are separated out and discussed.

23Na and 87Rb relaxation study of the structural phase transitions in the Tutton salts Na2Zn(SO4)2·6H2O and Rb2Zn(SO4)2·6H2O single crystals

AbstractThe NMR spectrum, spin–lattice relaxation times, T1, and the spin–spin relaxation times, T2, for the 23Na and 87Rb nuclei in Tutton salts Na2Zn(SO4)2·6H2O and Rb2Zn(SO4)2·6H2O single crystals were determined by using an FT NMR spectrometer. The NMR spectrum and relaxation times for the 23Na and 87Rb nuclei in two crystals undergo significant changes near TC. These changes close to TC were the only detectable result of the structural transformation; the change is due to the fact that the electric field gradient value becomes 0. Especially, T1 and T2 for 87Rb in the Rb2Zn(SO4)2·6H2O crystals at high temperature have similar values on the order of milliseconds, which is indicative of a liquid‐like system. The motion giving rise to this liquid‐like behavior is probably related to superionic motion at high temperature.

The EFG at sp-impurities in Zn and Cd—a new (final?) look

The electric field gradients (EFG) at the impurities Ni–Kr and Pd–Xe in the hcp metals Zn and Cd were calculated with the density functional code WIEN2k. Supercells with up to 150 atoms were used, resulting in a very good description of the available experimental data. Typical errors are 5–10%, with exceptions for Ag and Sb in Zn and for I in Zn and Cd, where a remeasurement is urged. The previously proposed systematic trend with positive EFG values for the first five impurity elements in every series and negative ones for the last three is confirmed.