$\mathit{Ab\!-\!initio}$ Determination of Magnetic Interface Coupling Constants for Magnetic Multilayers

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 C2v , C3v and other symmetry molecules of general formula MH2X2 and MHX3 , where the halogen atoms (X) are Cl, Br and I, and the heavy central atoms (M) are C and Si. The study presents results at a standardised level of calculation, triple-zeta in the valence space plus polarisation functions (TZVP) for the equilib-rium geometry stage; all-electron MP2 correlation is included in all these studies. For the bromo and iodo compounds, especially the latter, it is essential to allow core polarisation, by decontraction of the p,d-functions. This is conveniently done by initial optimization of the structure with a partly contract-ed basis, followed by reestablishment of the equilibrium structure with the decontracted basis.The NQCCs, derived from the EFGs, using the 'best' values for the atomic quadruple moments Cl, Br and I, lead to good agreement with the inertial axis (IA) data obtained from microwave spectroscopy. When the data from the present study is plotted against the values derived from the IA data, obtained by whatever approximations chosen by the MW authors, we obtain a linear regression for the data (85 points) with the slope 1.0365 and intercept -0.1737, with standard errors of 0.0042 and 0.2042, respectively; these are statistically identical results irrespective of whether the data is restricted to IA or EFG principal axis (PA) data.Since as in the C3v MH3X compounds studied previously, a close correlation of the microwave spectral data with the calculations was observed using the 'best' current values for Qz , there seems no need to postulate that the values of QBr for both 79Br and 81Br are seriously in error. A scaling downwards of Qz by about 5% for Br and I increases the agreement with experiment, but the contributions of relativistic effects are unknown, and could lead to further reassessment.Of the two common assumptions used in MW spectroscopy, to convert from IA to EFG-PA data, either (a) cylindrical symmetry of the NQCC along the bond direction, or (b) coincidence of the tensor principal element with the bond axis, the latter is found to be a much more realistic approximation.

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

Zeitschrift für Naturforschung A ◽

10.1515/zna-1998-6-719 ◽

1998 ◽

Vol 53 (6-7) ◽

pp. 383-395 ◽

Cited By ~ 2

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.

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New developments in the ab initio determination of transition metal alloys phase diagram

Journal de Chimie Physique ◽

10.1051/jcp/1993900249 ◽

1993 ◽

Vol 90 ◽

pp. 249-254 ◽

Cited By ~ 1

Author(s):

C Wolverton ◽

M Asta ◽

S Ouannasser ◽

H Dreyssé ◽

D de Fontaine

Keyword(s):

Phase Diagram ◽

Transition Metal ◽

Ab Initio ◽

Metal Alloys ◽

New Developments ◽

Transition Metal Alloys

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Ab initio structure determination of cytochrome c6 by combined reciprocal space-real space approach

Zeitschrift für Kristallographie - Crystalline Materials ◽

10.1524/zkri.218.1.68.20773 ◽

2003 ◽

Vol 218 (1) ◽

Author(s):

K. Chowdhury ◽

S. Ghosh ◽

M. Mukherjee

Keyword(s):

Cytochrome C ◽

Ab Initio ◽

Structure Determination ◽

Direct Method ◽

Real Space ◽

Reciprocal Space ◽

Cytochrome C6 ◽

Ab Initio Structure ◽

Space Approach

AbstractThe direct method program SAYTAN has been applied successfully to redetermine the structure of cytochrome c

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Determination of acidic dissociation constants of L-phenylalanyl-glycine and L-alanyl-L-alanine in water using ab initio methods

Hacettepe Journal of Biology and Chemistry ◽

10.15671/hjbc.20144210862 ◽

2014 ◽

Vol 2 (42) ◽

pp. 263-263

Author(s):

Farhoush Kiani ◽

Mahmoud Tajbakhsh ◽

Fereydoon Ashrafi ◽

Nesa Shafiei ◽

Azar Bahadori ◽

...

Keyword(s):

Ab Initio ◽

Dissociation Constants ◽

Ab Initio Methods ◽

Acidic Dissociation

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Gradient-Enhanced Inverse-Detected NMR Techniquesfor Determination of 1H-15N Coupling Constants in 2,2-Dimethylpenta-3,4-dienal Derivatives

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19971747 ◽

1997 ◽

Vol 62 (11) ◽

pp. 1747-1753 ◽

Cited By ~ 5

Author(s):

Radek Marek

Keyword(s):

Double Bond ◽

Chemical Shifts ◽

Multiple Bond ◽

Coupling Constants ◽

Single Quantum ◽

Nmr Techniques ◽

Phase Sensitive ◽

Heteronuclear Coupling

Determination of 15N chemical shifts and heteronuclear coupling constants of substituted 2,2-dimethylpenta-3,4-dienal hydrazones is presented. The chemical shifts were determined by gradient-enhanced inverse-detected NMR techniques and 1H-15N coupling constants were extracted from phase-sensitive gradient-enhanced single-quantum multiple bond correlation experiments. Stereospecific behaviour of the coupling constants 2J(1H,15N) and 1J(1H,13C) has been used to determine the configuration on a C=N double bond. The above-mentioned compounds exist predominantly as E isomers in deuteriochloroform.

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21,22-Disubstituted 18α,19βH-Ursane Derivatives with Oxabicyclooctane System in Ring E

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19930173 ◽

1993 ◽

Vol 58 (1) ◽

pp. 173-190 ◽

Cited By ~ 1

Author(s):

Eva Klinotová ◽

Jiří Klinot ◽

Václav Křeček ◽

Miloš Buděšínský ◽

Bohumil Máca

Keyword(s):

Spectral Data ◽

Spin Systems ◽

Coupling Constants ◽

Complete Analysis ◽

Nmr Spectrum ◽

Proton Proton ◽

H Nmr ◽

Proton Coupling ◽

C Nmr

Reaction of 3β-acetoxy-21,22-dioxo-18α,19βH-ursan-28,20β-olide (IIIa) and 20β,28-epoxy-21,22-dioxo-19α,19βH-ursan-3β-yl acetate (IIIb) with diazomethane afforded derivatives XII-XIV with spiroepoxide group in position 21 or 22, which were further converted into hydroxy derivatives XV and XVII. Ethylene ketals VIII-X were also prepared. In connection with the determination of position and configuration of the functional groups at C(21) and C(22), the 1H and 13C NMR spectral data of the prepared compounds are discussed. Complete analysis of two four-spin systems in the 1H NMR spectrum of bisethylenedioxy derivative Xb led to the proton-proton coupling constants from which the structure with two 1,4-dioxane rings condensed with ring E, and their conformation, was derived.

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New high-pressure phases of Fe7N3 and Fe7C3 stable at Earth's core conditions: evidences for carbon–nitrogen isomorphism in Fe-compounds

RSC Advances ◽

10.1039/c8ra09942a ◽

2019 ◽

Vol 9 (7) ◽

pp. 3577-3581 ◽

Cited By ~ 5

Author(s):

Nursultan Sagatov ◽

Pavel N. Gavryushkin ◽

Talgat M. Inerbaev ◽

Konstantin D. Litasov

Keyword(s):

Crystal Structure ◽

High Pressure ◽

Ab Initio ◽

Structure Prediction ◽

Harmonic Approximation ◽

Crystal Structure Prediction ◽

Earth’S Core ◽

Earth's Core ◽

Core Conditions

We carried out ab initio calculations on the crystal structure prediction and determination of P–T diagrams within the quasi-harmonic approximation for Fe7N3 and Fe7C3.

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