Search results for "Coupling"
showing 10 items of 1862 documents
Global nuclear structure aspects of tensor interaction
2008
A direct fit of the isoscalar spin-orbit and both isoscalar and isovector tensor coupling constants to the f5/2-f7/2 SO splittings in 40Ca, 56Ni, and 48Ca requires: (i) a significant reduction of the standard isoscalar spin-orbit strength and (ii) strong attractive tensor coupling constants. The aim of this paper is to address the consequences of these strong attractive tensor and weak spin-orbit fields on total binding energies, two-neutron separation energies and nuclear deformability.
Prediction of water's isotropic nuclear shieldings and indirect nuclear spin–spin coupling constants (SSCCs) using correlation‐consistent and polariz…
2009
Density functional theory (DFT) was used to estimate water's isotropic nuclear shieldings and indirect nuclear spin-spin coupling constants (SSCCs) in the Kohn-Sham (KS) complete basis set (CBS) limit. Correlation-consistent cc-pVxZ and cc-pCVxZ (x = D, T, Q, 5, and 6), and their modified versions (ccJ-pVxZ, unc-ccJ-pVxZ, and aug-cc-pVTZ-J) and polarization-consistent pc-n and pcJ-n (n = 0, 1, 2, 3, and 4) basis sets were used, and the results fitted with a simple mathematical formula. The performance of over 20 studied density functionals was assessed from comparison with the experiment. The agreement between the CBS DFT-predicted isotropic shieldings, spin-spin values, and the experimenta…
Energy landscape properties studied using symbolic sequences
2006
We investigate a classical lattice system with $N$ particles. The potential energy $V$ of the scalar displacements is chosen as a $\phi ^4$ on-site potential plus interactions. Its stationary points are solutions of a coupled set of nonlinear equations. Starting with Aubry's anti-continuum limit it is easy to establish a one-to-one correspondence between the stationary points of $V$ and symbolic sequences $\bm{\sigma} = (\sigma_1,...,\sigma_N)$ with $\sigma_n=+,0,-$. We prove that this correspondence remains valid for interactions with a coupling constant $\epsilon$ below a critical value $\epsilon_c$ and that it allows the use of a ''thermodynamic'' formalism to calculate statistical prope…
13C nuclear magnetic resonance study of some phosphinolipids: Assignments and conformational studies
1989
13C chemical shifts and 31P, 13C spin-spin coupling constants are reported for six model phosphinates and eight synthetic phosphinolipids. The complex spectra of the synthetic phosphinolipids could be assigned from increments and couplings derived from the model compounds. Based on these investigations the 3J(PC) couplings of 7–15 Hz indicate a preferential trans orientation of the respective head-group carbon relative to the phosphorus. This behaviour is similar to that of natural phosphatidylcholine lipids.
17O NMR and molecular mechanical studies of arylmethylenemalonaldehydes
1990
The 17O NMR spectra of six different arylmethylenemalonaldehydes were measured for various solvents and temperatures. The 17O NMR chemical shifts and line widths of the carbonyl oxygens of the malonaldehyde fragment show a clear variation in the series of monoaryl compounds studied. The differences between the 17O NMR chemical shifts of the formyl oxygens correlate well with two conformationally dependent 1H–1H and 1H–13C coupling constants for the same compounds. Molecular mechanical calculations were also performed in order to relate the present data with the conformational preferences of the malonaldehyde fragment of the arylmethylenemalonaldehydes.
The route to high accuracy in ab initio calculations of Cu quadrupole-coupling constants.
2012
We report nonrelativistic and scalar-relativistic coupled-cluster calculations of the copper quadrupole-coupling constants for eleven small copper-containing compounds. It is shown to be necessary to treat both electron-correlation and scalar-relativistic effects on the same footing even for a qualitatively correct description, because both effects are significant and are strongly coupled in the case of Cu electric-field gradients. We show that the three scalar-relativistic schemes employed in the present study--the leading order of direct perturbation theory, the spin-free exact two-component theory in its one-electron variant, and the spin-free Dirac-Coulomb approach--provide accurate tre…
[(Pyridylcarbonyl)pyridyl]triazolopyridines, Useful Ligands for the Construction of Polynuclear Coordination Compounds – Synthesis, Crystal Structure…
2007
A new tetranuclear cubane Cu4O4 complex has been synthesised from assembly of CuII ions and the polydentate ligand (pyridin-2-yl){6-([1,2,3]triazolo[1,5-a]pyridin-3-yl)pyridin-2-yl}methanone. Crystallographic analysis indicates that the Cu4O4 unit has an S4 symmetry. The magnetic properties have been analysed using the H = –2Σi,jJijSiSj spin Hamiltonian. Two distinct coupling constants, 2J1,3 = –37.4 cm–1 and 2J1,2 = –2.6 cm–1, obtained from the fitting of the experimental data have been rationalised on the basis of a density functional study of magnetostructural correlations in cubane complexes containing the Cu4O4 core. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Synthesis, spectroscopic and conformational analysis of 1,4-dihydroisonicotinic acid derivatives
2014
Abstract Structural and conformational properties of 1,4-dihydroisonicotinic acid derivatives, characterized by ester, ketone or cyano functions at positions 3 and 5 in solid and liquid states have been investigated by X-ray analysis and nuclear magnetic resonance and supported by quantum chemical calculations. The dihydropyridine ring in each of the compounds exists in flattened boat-type conformation. The observed ring distortions around the C(4) and N(1) atoms are interrelated. The substituent at N(1) has great influence on nitrogen atom pyramidality. The 1H, 13C and 15N NMR chemical shifts and coupling constants are discussed in terms of their relationship to structural features such as…
Relativistic DFT Calculation of (119)Sn Chemical Shifts and Coupling Constants in Tin Compounds.
2006
The nuclear shielding and spin-spin coupling constants of (119)Sn in stannane, tetramethylstannane, methyltin halides Me4-nSnXn (X = Cl, Br, I; n = 1-3), tin halides, and some stannyl cations have been investigated computationally by DFT methods and Slater all-electron basis sets, including relativistic effects by means of the zeroth order regular approximation (ZORA) method up to spin-orbit coupling. Calculated (119)Sn chemical shifts generally correlate well with experimental values, except when several heavy halogen atoms, especially iodine, are bound to tin. In such cases, calculated chemical shifts are almost constant at the scalar (spin-free) ZORA level; only at the spin-orbit level i…
Complete basis set prediction of methanol isotropic nuclear magnetic shieldings and indirect nuclear spin-spin coupling constants (SSCC) using polari…
2009
Efficient B3LYP and BHandH density functionals were used to estimate methanol's nuclear magnetic isotropic shieldings and spin–spin coupling constants in the basis set limit. Polarization-consistent pcS-n and pcJ-n (n = 0, 1, 2, 3 and 4), and segmented contracted XZP, where X = D, T, Q and 5, basis sets were used and the results fitted with simple mathematical formulas. The performance of the methods was assessed from comparison with experiment and higher level calculations. 1J(CH) and 3J(HH) values were determined from very diluted solutions in deuterochloroform and compared with theoretical predictions. The agreement between complete basis set (CBS) density functional theory (DFT) predict…