scholarly journals Fast and Accurate Electric Field Gradient Calculations in Molecular Solids With Density Functional Theory

2021 ◽  
Vol 9 ◽  
Author(s):  
Joshua D. Hartman ◽  
Amanda Mathews ◽  
James K. Harper
Keyword(s):  
Plane Wave ◽  
Electric Field ◽  
Electric Field Gradient ◽  
Field Gradient ◽  
Single Molecule ◽  
Density Functional ◽  
Coupling Constants ◽  
Molecular Solids ◽  
Density Functionals ◽  
Periodic Calculations

Modern approaches for calculating electric field gradient (EFF) tensors in molecular solids rely upon plane-wave calculations employing periodic boundary conditions (PBC). In practice, models employing PBCs are limited to generalized gradient approximation (GGA) density functionals. Hybrid density functionals applied in the context of gauge-including atomic orbital (GIAO) calculations have been shown to substantially improve the accuracy of predicted NMR parameters. Here we propose an efficient method that effectively combines the benefits of both periodic calculations and single-molecule techniques for predicting electric field gradient tensors in molecular solids. Periodic calculations using plane-wave basis sets were used to model the crystalline environment. We then introduce a molecular correction to the periodic result obtained from a single-molecule calculation performed with a hybrid density functional. Single-molecule calculations performed using hybrid density functionals were found to significantly improve the agreement of predicted 17O quadrupolar coupling constants (Cq) with experiment. We demonstrate a 31% reduction in the RMS error for the predicted 17O Cq values relative to standard plane-wave methods using a carefully constructed test set comprised of 22 oxygen-containing molecular crystals. We show comparable improvements in accuracy using five different hybrid density functionals and find predicted Cq values to be relatively insensitive to the choice of basis set used in the single molecule calculation. Finally, the utility of high-accuracy 17O Cq predictions is demonstrated by examining the disordered 4-Nitrobenzaldehyde crystal structure.

AlN Nanotubes: A DFT Study of Al-27 and N-14 Electric Field Gradient Tensors

2007 ◽  
Vol 62 (12) ◽  
pp. 711-715 ◽  
Author(s):  
Ahmad Seif ◽  
Mahmoud Mirzaei ◽  
Mehran Aghaie ◽  
Asadollah Boshra
Keyword(s):  
Electric Field ◽  
Electric Field Gradient ◽  
Field Gradient ◽  
Density Functional ◽  
Quadrupole Coupling Constant ◽  
Basis Set ◽  
Basis Sets ◽  
B3lyp Method ◽  
Package Program ◽  
Nqr Parameters

Density functional theory (DFT) calculations were performed to calculate the electric field gradient (EFG) tensors at the sites of aliminium (27Al) and nitrogen (14N) nuclei in an 1 nm of length (6,0) single-walled aliminium nitride nanotube (AlNNT) in three forms of the tubes, i. e. hydrogencapped, aliminium-terminated and nitrogen-terminated as representatives of zigzag AlNNTs. At first, each form was optimized at the level of the Becke3,Lee-Yang-Parr (B3LYP) method, 6-311G∗∗ basis set. After, the EFG tensors were calculated at the level of the B3LYP method, 6-311++G∗∗ and individual gauge for localized orbitals (IGLO-II and IGLO-III) types of basis sets in each of the three optimized forms and were converted to experimentally measurable nuclear quadrupole resonance (NQR) parameters, i. e. quadrupole coupling constant (qcc) and asymmetry parameter (ηQ). The evaluated NQR parameters revealed that the considered model of AlNNT can be divided into four equivalent layers with similar electrostatic properties.With the exception of Al-1, all of the three other Al layers have almost the same properties, however, N layers show significant differences in the magnitudes of the NQR parameters in the length of the nanotube. Furthermore, the evaluated NQR parameters of Al-1 in the Al-terminated form and N-1 in the N-terminated form revealed the different roles of Al (base agent) and of N (acid agent) in AlNNT. All the calculations were carried out using the GAUSSIAN 98 package program.

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.

The Electric Field Gradient at the Site of the Halogen Ion and Structure of Amino Acid Hydrobromides and Hydroiodides

1992 ◽  
Vol 47 (7-8) ◽  
pp. 887-917
Author(s):  
Armin Kehrer ◽  
Shi-qi Dou ◽  
Alarieh Weiss
Keyword(s):  
Electric Field ◽  
Electric Field Gradient ◽  
Field Gradient ◽  
Room Temperature ◽  
Low Frequency ◽  
Coupling Constants ◽  
Coupling Constant ◽  
Resonance Frequencies ◽  
Quadrupole Coupling ◽  
Frequency Coupling

Abstract The 79,81Br and 127I NQR spectra of several hydrobromides, respectively hydroiodides, of amino acides and dipeptides were studied, mostly as functions of temperature in the range 77 < T/K <420. The investigated compounds are: L-Arg • HBr • H2O, L-Cys • HBr • H2O , L - Cys - S - S - L - Cys • 2HBr, ethanolamine • HBr, L-Glu • HBr, L-His • HBr, L-His • 2HBr, L-Ile HBr • H2O , Sar • HBr, (Sar)2 • HBr, L-Val • HBr • H2O , Gly • LiBr, Gly-Gly • LiBr, ethanolamine HI, Sar • HI, (Sar)2 • HI, (Gly)2 • HI, (L-Val)2 • HI, Gly-L-Leu • HI • H2O . A phase transition with hysteresis was observed for L-Val • HBr • H2O (Tc.up = 318 K, Tc.down = 242 K). Two solid phases of Sar • HI have been studied by NQR, one crystallized from melt, the other one from aqueous solution. For three of the title compounds the crystal structure was determined at room temperature: L-His - 2HBr, P212121 , Z = 4, aj pm = 1652, b/pm = 916, c/pm = 721; L-Cys HBr H2O , P212121 , Z = 4, a/pm = 1955, b/pm = 746, c/pm = 550; Gly-L-Leu • HI • H2O , P2X, Z = 2, a / p m = 1289, b/pm = 914, c/pm = 615, ß/° = 99.In most cases the halogen ion in the studied hydrohalides is polycoordinated by hydrogen bonds of the type N - H • • • X⊖ and O - H • • • X⊖ , X = Br, I. The NQR frequencies and, for iodine, the nuclear quadrupole coupling constants depend on this coordination. A low frequency (coupling constant) region is found for pure N - H • • • X⊖ coordination. Replacing one N - H • • • X⊖ bond by O - H • • • X⊖ rises the electric field gradient, EFG, respectively the resonance frequencies. The dependence of the EFG on the hydrogen bond coordination N - H • • • X⊖ plus O - H • • • X⊖ is discussed for the title compounds including information from literature

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