Modeling Substituent-Dependence of the Twist and Shielding in a Series of 4-Substituted N-(4-Nitrobenzylidene)anilines

2004 ◽  
Vol 69 (8) ◽  
pp. 1566-1576 ◽  
Author(s):  
Vladimír Proks ◽  
Miroslav Holík
Keyword(s):  
Chemical Shift ◽  
Ab Initio ◽  
Density Functional ◽  
Ring Current ◽  
Functional Theory ◽  
H Nmr ◽  
Current Contribution ◽  
Monosubstituted Benzenes ◽  
Experimental Chemical Shift

A series of 15 4-substituted N-(4-nitrobenzylidene)anilines was synthesized and studied by 1H NMR spectroscopy. Their ab initio calculated geometries and the shielding as expressed by aromatic ring currents were used in correlation analysis. The geometries were fully optimized using density functional theory B3LYP/6-311G** approaches. For the determination of the ring current contribution to the shielding of azomethine hydrogens Hα was used direct ab initio calculation of the chemical shielding in a model system. Experimental chemical shift values free of these contributions were successfully correlated with increments ap of chemical shift for monosubstituted benzenes. In the same manner, the contribution of the anisotropy of C=N double bond to Hm hydrogen were calculated and values of the Hm chemical shift free of this contribution were successfully correlated with increments of chemical shift am.

Calculations of Surface Structure for SrTiO3 Perovskite

2001 ◽  
Vol 672 ◽  
Author(s):  
E. Heifetsa ◽  
R.I. Eglitisb ◽  
E.A. Kotomin ◽  
G. Borstelb
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Dipole Moments ◽  
Surface Relaxation ◽  
Surface Layers ◽  
Functional Theory ◽  
Near Surface ◽  
Hartree Fock ◽  
Semi Empirical

ABSTRACTWe present and discuss results of the calculations for SrTiO3 (100) surface relaxation with different terminations (SrO and TiO2) using a semi-empirical shell model (SM) as well as abinitio methods based on Hartree-Fock (HF) and Density Functional Theory (DFT) formalisms. Using the SM, the positions of atoms in 16 near-surface layers placed atop a slab of rigid ions are optimized. This permits us determination of surface rumpling and surfaceinduced dipole moments (polarization) for different terminations. We also compare results of the ab initio calculations based on both HF with the DFT-type electroncorrelation corrections, several DFT with different exchange-correlation functionals, and hybrid exchange techniques. OurSM results for the (100) surfaces are in a good agreement with both our ab initio calculations and LEED experiments.

Hydrogenation of Nanodiamond Surfaces: Structure and Effects on Crystalline Stability

2003 ◽  
Vol 10 (02n03) ◽  
pp. 233-239 ◽  
Author(s):  
S. P. Russo ◽  
A. S. Barnard ◽  
I. K. Snook
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Atomic Layer ◽  
Parallel Computer ◽  
Generalized Gradient ◽  
Functional Theory ◽  
First Approximation ◽  
The Stability ◽  
Bulk Diamond

Presented are results of our ab initio study of the surface reconstruction and relaxation of (100) surfaces on bulk and nanocrystalline diamond. We have used a density functional theory (DFT) within the generalized-gradient approximation (GGA) via the parallel computer version of the Vienna ab initio simulation package (VASP), to consider dehydrogenated and hydrogenated surfaces. Edges and corners of nanocrystals offer a new challenge in the determination of surface structure. We have applied the methodology for stepped diamond (100) surfaces to this problem, and consider it useful in describing nanodiamond edges and corners to first approximation. Our results also indicate that dimer lengths and atomic layer depths of the C(100)(2 × 1) and C(100)(2 × 1):H nanodiamond surfaces differ slightly from those of bulk diamond. The effects of these differences on crystalline stability are discussed, with the intension of offering a better understanding of the effects of nanodiamond surfaces on the stability of diamondoid nanostructures.

A Combined ab initio and Density Functional Study of the Electronic Structure of Thymine and 2-Thiothymine Radicals

2003 ◽  
Vol 68 (12) ◽  
pp. 2322-2334 ◽  
Author(s):  
Robert Vianello ◽  
Zvonimir B. Maksić
Keyword(s):  
Ab Initio ◽  
Spin Density ◽  
Density Functional ◽  
Radical Cations ◽  
Functional Study ◽  
Theory Approach ◽  
Functional Theory ◽  
Adiabatic Ionization Potential ◽  
Highest Occupied Molecular Orbital ◽  
Positively Charged

The electronic and energetic properties of thymine (1) and 2-thiothymine (2) and their neutral and positively charged radicals are considered by a combined ab initio and density functional theory approach. It is conclusively shown that ionization of 1 and 2 greatly facilitates deprotonation of the formed radical cations thus making the proton transfer between charged and neutral precursor species thermodynamically favourable. The adiabatic ionization potential of 1 and 2 are analysed. It appears that ADIP(1) is larger than ADIP(2) by 10 kcal/mol, because of greater stability of the highest occupied molecular orbital (HOMO) of the former. It is also shown beyond any doubt that the spin density in neutral and cationic radical of 2 is almost exclusively placed on the σ-3p AO of sulfur implying that these two systems represent rather rare sigma-radicals. In contrast, the spin density of radicals of 1 is distributed over their π-network.

Ab Initio Calculation of Mechanical Properties of Stacking Fault in 3C-SiC: Effect of Stress and Doping

2012 ◽  
Vol 717-720 ◽  
pp. 415-418
Author(s):  
Yoshitaka Umeno ◽  
Kuniaki Yagi ◽  
Hiroyuki Nagasawa
Keyword(s):  
Mechanical Properties ◽  
Ab Initio ◽  
Density Functional ◽  
Stacking Faults ◽  
Single Layer ◽  
Local Strain ◽  
Density Functional Theory Calculations ◽  
Stacking Fault ◽  
Functional Theory ◽  
N Doping

We carry out ab initio density functional theory calculations to investigate the fundamental mechanical properties of stacking faults in 3C-SiC, including the effect of stress and doping atoms (substitution of C by N or Si). Stress induced by stacking fault (SF) formation is quantitatively evaluated. Extrinsic SFs containing double and triple SiC layers are found to be slightly more stable than the single-layer extrinsic SF, supporting experimental observation. Effect of tensile or compressive stress on SF energies is found to be marginal. Neglecting the effect of local strain induced by doping, N doping around an SF obviously increase the SF formation energy, while SFs seem to be easily formed in Si-rich SiC.

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