The ab initio Calculation of Nuclear Quadrupole Coupling Constants with Special Reference to 33S

1992 ◽  
Vol 47 (1-2) ◽  
pp. 203-216 ◽  
Author(s):  
Michael H. Palmer
Keyword(s):  
Experimental Data ◽  
Ab Initio ◽  
Ab Initio Calculation ◽  
Coupling Constants ◽  
Basis Set ◽  
Equilibrium Geometry ◽  
Relaxation Methods ◽  
Quadrupole Coupling ◽  
Nuclear Quadrupole ◽  
The Relationship

AbstractThe ab initio calculation of 33S nuclear quadrupole coupling constants (NQCC) for a range of S-containing compounds with S2, S4 and S6 bonding types is described. All of the calculations used a triple zeta valence + polarisation basis set (TZVP) of gaussian type orbitals; all of the molecules were studied at the TZVP equilibrium geometry. The electric field gradients (EFG) calculated were correlated with the experimental NQCC obtained by either microwave spectroscopy (MW), nuclear quadrupole resonance (NQR) or NMR relaxation methods; although the experimental data cover a wide diversity of chemical types over a long period of time, the slope of the relationship between the EFG (qii) and the NQCC (χii) yields a value for the 33S atomic quadrupole moment of - 0.064 barn, very close to recent calculations with a large atomic basis set, and to experimental data. The relationship between the EFG tensor components and the internal molecular structure features is discussed for a diverse series of molecules.

Halogen Nuclear Quadrupole Coupling Constants: Comparison of ab initio Calculations which include Correlation, with Experiment

1998 ◽  
Vol 53 (6-7) ◽  
pp. 383-395 ◽  
Author(s):  
Michael H. Palmer ◽  
John A. Blair-Fish ◽  
Paul Sherwood ◽  
Martyn F. Guest
Keyword(s):  
Ab Initio ◽  
Close Correlation ◽  
Coupling Constants ◽  
Basis Set ◽  
Equilibrium Geometry ◽  
Quadrupole Moments ◽  
Axially Symmetric ◽  
Quadrupole Coupling ◽  
Nuclear Quadrupole

Abstract Ab initio determination of the electric field gradient (EFG) tensors at halogen and other centres ena-bled determination of the nuclear quadrupole coupling constants (NQCC) for a diverse set of axially symmetric (C3v , C∞v, D∞h and other symmetries) inorganic and organic molecules, where the heavy ele-ments are Cl, Br, and I with C, Si, Ge, and Sn hydrides. The latter elements are in an approximately tetrahedral environment. The study presents results at a standardised level of calculation, triple-zeta in the valence space (TZV) plus polarisation functions (TZVP) for the equilibrium geometry stage; all-electron MP2 correlation is included in all these studies. f-Orbital exponents were optimised for both Br and I centres in the methanes; the atomic populations of the f-orbital components are very small for the Br-and I-atoms, confirming their role as polarisation functions rather than having any bonding character. The EFG are determined at equilibrium with the TZVP basis set, except Sn and I centres where the basis set is TZV + MP2. For the bromo and iodo compounds, especially the latter, it is essential to allow for core polarisation, by decontraction of the p,d-functions. This is conveniently done by initial optimization of the structure with a partly contracted basis, followed by reestablishment of the equilibrium structure with the decontracted basis. A close correlation of the observed (microwave spectral) data with the calculations was observed, using the 'best' values for the atomic quadrupole moments for Cl, Br, and I; thus there seems no need to postulate that the value of QBr for 79Br and 81Br are in error. The SCF and MP2 wave-functions were converted into localised molecular orbitals by the Boys Method. This allowed a study of the differing s/p/d-hybridisation ratios, and the centroid positions, to be compared with the quadrupole coupling constants. The charge distributions for the atoms were converted into local bond dipoles, which in turn are correlated with the electronegativity differences of the bonded atoms.

14N Nuclear Quadrupole Coupling in Glycyl-Glycine and Related Peptides

1984 ◽  
Vol 39 (11) ◽  
pp. 1108-1111 ◽  
Author(s):  
Michael Palmer
Keyword(s):  
Crystal Structure ◽  
Ab Initio ◽  
Ab Initio Calculation ◽  
Coupling Constants ◽  
Double Zeta ◽  
Quadrupole Coupling ◽  
Aromatic Systems ◽  
Nuclear Quadrupole ◽  
Glycyl Glycine

An ab initio calculation of double zeta quality on glycyl-glycine at the crystal structure yielded nuclear quadrupole coupling constants at the peptide centres very close to experiment; Xzz -3.03, Xyy +2.14, Xxx +0.89 MHz. The first two couplings lie in the local π-direction, and along the C-N bond, respectively. At the NH⊕3 centre the values were less satisfactory, but the (low) positive value of Xzz was obtained, and lies relatively close to the N-C bond. The results suggest that similar calculations may be successful for other H-bonded systems, provided that aromatic systems are not involved.

The ab initio Calculation of Nuclear Quadrupole Coupling Constants and their Comparison with Experiment

1990 ◽  
Vol 45 (3-4) ◽  
pp. 357-367 ◽  
Author(s):  
Michael H. Palmer
Keyword(s):  
Ab Initio ◽  
Single Molecule ◽  
Ab Initio Calculation ◽  
Coupling Constants ◽  
Structural Variations ◽  
Electric Field Gradients ◽  
Field Gradients ◽  
Comparison With Experiment ◽  
Quadrupole Coupling ◽  
Nuclear Quadrupole

Abstract Ab initio calculations of electric field gradients (EFG) and conversion to nuclear quadrupole coupling constants (NQCC) are described, with particular reference to 14 N and 10,11B. The correlation of EFG and NQCC for a series of boranes leads to the value 8.32 MHz/a.u. (0.0354 barn) for Q(11B). The structural variations of these microwave and single molecule calculations of 10,11 B NQCC are discussed.

Ab initio Study of Nitrogen-14 Nuclear Quadrupole Coupling and NMR Signal Linewidths in Some Azoles

1998 ◽  
Vol 53 (6-7) ◽  
pp. 362-369 ◽  
Author(s):  
Michał Jaszuński ◽  
Antonio Rizzo
Keyword(s):  
Ab Initio ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Basis Set ◽  
Quadrupole Coupling ◽  
Spin Coupling Constants ◽  
Nuclear Quadrupole ◽  
Spin Spin Coupling ◽  
Nmr Properties ◽  
Nmr Signals

Abstract Ab initio values of Nitrogen 14N Nuclear Quadrupole Coupling Constants (NQCC's) are calculated for a series of methyl-substituted azoles in the Multiconfigurational SCF (MCSCF) approximation. The four triazoles and two tetrazoles studied here are all isoelectronic. This enabled us to use the same level of approximation - basis set and active space -for all the molecules. The computed NQCC's are used to estimate the relative widths of the 14N NMR signals, assuming an identical effect of molecular tumbling for all the nuclei in a molecule and neglecting solvent effects. The linewidths for the unsubstituted N atoms are, in agreement with experiment, much larger than for the methyl-substituted N atom. For the 1-methyl-tetrazole we present also the NMR shielding and spin-spin coupling constants and discuss in some more detail the dependence of all calculated NMR properties on the basis set and correlation effects.

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