Density Functional Theory Investigation of Hydrogen Bonding Effects on the Oxygen, Nitrogen and Hydrogen Electric Field Gradient and Chemical Shielding Tensors of Anhydrous Chitosan Crystalline Structure

2007 ◽  
Vol 111 (5) ◽  
pp. 963-970 ◽  
Author(s):  
Mehdi D. Esrafili ◽  
Fatemeh Elmi ◽  
Nasser L. Hadipour
Keyword(s):  
Density Functional Theory ◽  
Hydrogen Bonding ◽  
Electric Field ◽  
Electric Field Gradient ◽  
Field Gradient ◽  
Crystalline Structure ◽  
Density Functional ◽  
Chemical Shielding ◽  
Functional Theory ◽  
Shielding Tensors

The C–H···O Hydrogen Bonding Effects on the 17O Electric Field Gradient and Chemical Shielding Tensors in Crystalline 1-Methyluracil: A DFT Study

2006 ◽  
Vol 61 (7-8) ◽  
pp. 383-388 ◽  
Author(s):  
Tayyebeh Partovi ◽  
Mahmoud Mirzaei ◽  
Nasser L. Hadipour
Keyword(s):  
Hydrogen Bonding ◽  
Electric Field ◽  
Electric Field Gradient ◽  
Field Gradient ◽  
Density Functional ◽  
Geometry Optimization ◽  
Neutron Diffraction Study ◽  
Functional Study ◽  
Chemical Shielding ◽  
Shielding Tensors

A density functional study was carried out to investigate the C-H···O hydrogen bonding effects on the 17O electric field gradient and chemical shielding tensors in crystalline 1-methyluracil. Since the structural coordinates were obtained from a neutron diffraction study, no geometry optimization was needed in performing the calculations. It is demonstrated that C-H···O hydrogen bonding has different influences on O2 and O4 EFG and CS tensors. In the tetramer model of 1-methyluracil, which is much closer to the real crystalline phase, the influence of C-H···O on the O4 EFG and CS tensors is significant, whereas this influence is negligible for O2.

DENSITY FUNCTIONAL THEORY STUDY OF BINDING ENERGIES, 7Li NUCLEAR MAGNETIC SHIELDING, AND ELECTRIC FIELD GRADIENT TENSORS ON THE SMALL CLUSTERS OF LinHm (m ≤ n ≤ 4)

2007 ◽  
Vol 06 (04) ◽  
pp. 959-973 ◽  
Author(s):  
MEHDI D. ESRAFILI ◽  
FATEMEH ELMI ◽  
NASSER L. HADIPOUR
Keyword(s):  
Density Functional Theory ◽  
Electric Field ◽  
Electric Field Gradient ◽  
Field Gradient ◽  
Density Functional ◽  
Three Dimensional ◽  
Lithium Hydride ◽  
Binding Energies ◽  
Magnetic Shielding ◽  
Functional Theory

The binding energies, geometries, 7 Li magnetic shielding, and electric field gradient tensors of hydrogenated lithium clusters, Li n H m (m ≤ n ≤ 4), were studied via density functional theory approach. We optimized the structures using B3LYP functional and 6-311++G (2d,2p) basis set. The calculated binding energies of lithium hydride clusters indicate that hydrogenation energy of Li n H m clusters decreases as the number of hydrogen atoms within the cluster increases. Our calculations also showed that for n = 4 clusters, the three-dimensional structure is more stable than the planar one. The study of the trends in the 7 Li magnetic shielding isotropy, σiso, and anisotropies, Δσ, values are explained in terms of the interplay between the electronic and geometrical effects. The variations in the 7 Li nuclear quadrupole coupling constants, χ, and their associated asymmetry parameters, ηQ, for different isomers of the lithium hydride clusters and the influence of hydrogenation on the EFG tensors are also discussed. For n = 4, we obtained a noticeable difference in the χ value from the planar to the three-dimensional structures. The atoms in molecules (AIM) analysis at the Li–H bond critical point reveals remarkably different topographical properties of the charge density and associated Laplacian fields for the planar and three-dimensional lithium hydride clusters.

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