scholarly journals J-coupling constants for a trialanine peptide as a function of dihedral angles calculated by density functional theory over the full Ramachandran space

2011 ◽  
Vol 13 (39) ◽  
pp. 17484 ◽  
Author(s):  
Pedro Salvador ◽  
I-Hsien (Midas) Tsai ◽  
J. J. Dannenberg
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Coupling Constants ◽  
Dihedral Angles ◽  
Functional Theory ◽  
J Coupling ◽  
J Coupling Constants

Assessing the Calculation of Exchange Coupling Constants and Spin Crossover Gaps Using the Approximate Projection Model to Improve Density Function Calculations

2019 ◽  
Author(s):  
Xianghai Sheng ◽  
Lee Thompson ◽  
Hrant Hratchian
Keyword(s):  
Density Functional Theory ◽  
Exchange Coupling ◽  
Density Functional ◽  
Spin Crossover ◽  
Coupling Constants ◽  
Spin Projection ◽  
Coupling Constant ◽  
Projection Model ◽  
Functional Theory

This work evaluates the quality of exchange coupling constant and spin crossover gap calculations using density functional theory corrected by the Approximate Projection model. Results show that improvements using the Approximate Projection model range from modest to significant. This study demonstrates that, at least for the class of systems examined here, spin-projection generally improves the quality of density functional theory calculations of J-coupling constants and spin crossover gaps. Furthermore, it is shown that spin-projection can be important for both geometry optimization and energy evaluations. The Approximate Project model provides an affordable and practical approach for effectively correcting spin-contamination errors in molecular exchange coupling constant and spin crossover gap calculations.

Hexaethyl-2,4-dicarba-nido-hexaborane(8), Deprotonation and Complexation Studied by NMR Spectroscopy and Density Functional Theory (DFT) Calculations

2004 ◽  
Vol 59 (6) ◽  
pp. 685-691 ◽  
Author(s):  
Bernd Wrackmeyer ◽  
Hans-Jörg Schanz
Keyword(s):  
Density Functional Theory ◽  
Nmr Spectroscopy ◽  
Density Functional ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Analogous Reaction ◽  
Sandwich Complex ◽  
Dft Methods ◽  
Functional Theory ◽  
Nmr Data

Deprotonation of hexaethyl-2,4-dicarba-nido-borane(8) 2 leads first to the hexaethyl-2,4-dicarbanido- borate(1−) 3, and further deprotonation, using BuLi/KOtBu, gives the hexaethyl-2,4-dicarbanido- hexaborate(2−) 4. The reaction of 3 with FeCl2 affords the commo-ferracarborane [Fe(Et6-2,4- C2B4H)2] 5, and the analogous reaction of 4 leads to the anionic sandwich complex [Fe(Et6-2,4- C2B4)2]2− 6 which can be protonated to give 5. The complex 5 contains two hydrido ligands, each bridging the iron and two boron atoms. Reactions were monitored and the products were characterised by 11B NMR spectroscopy in solution. The geometries of the carboranes, the borates (all unsubstituted and permethyl-substituted) and the iron complexes (all unsubstituted) were optimised by DFT methods [B3LYP/6-311+G(d,p) or B3LYP/6-31+G(d)], and the relevant NMR data [chemical shifts δ11B, δ13C, δ57Fe, and coupling constants 1J(13C,1H), 1J(11B,1H), 1J(57Fe,1H), 1J(57Fe,11B)] were calculated at the same level of theory.

Twisted Push - Pull Ethylenes

2008 ◽  
Vol 61 (10) ◽  
pp. 805 ◽  
Author(s):  
Rakesh Naduvile Veedu ◽  
Paul V. Bernhardt ◽  
Rainer Koch ◽  
Curt Wentrup
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Room Temperature ◽  
Dihedral Angles ◽  
Functional Theory ◽  
Activation Barriers ◽  
Rapid Rotation ◽  
X Ray ◽  
X Ray Crystallography ◽  
Calculated Activation

As determined by X-ray crystallography, Meldrum’s acid derivatives 5, 6, and 8 feature dihedral angles around the central C5=C7 double bond of 14–35°, whereas for the anion 9 this angle is 90°. Density functional theory and MP2 calculations are in agreement with the experimental X-ray data for compounds 5–8, but for anion 9 an angle of only ~65° is predicted. It is concluded that a part of the torsion is due to packing forces in the crystal. It is further concluded that these molecules undergo rapid rotation about the central CC bonds at room temperature (calculated activation barriers 5–14 kcal mol–1).

A density functional theory approach to the magnetic properties of a coupled single-molecule magnet (Mn7)2 complex — An entangled qubit pair candidate

2013 ◽  
Vol 91 (9) ◽  
pp. 866-871 ◽  
Author(s):  
Silvia Gómez-Coca ◽  
Eliseo Ruiz
Keyword(s):  
Density Functional Theory ◽  
Single Molecule ◽  
Exchange Coupling ◽  
Density Functional ◽  
Relative Strength ◽  
Coupling Constants ◽  
Basis Set ◽  
Theory Approach ◽  
Functional Theory ◽  
Spin Configuration

The exchange coupling constants of a Mn14 complex constituted by two weakly coupled Mn7 moieties were calculated using two different density functional theory (DFT) approaches: the Perdew–Burke–Ernzerhof (PBE) functional with a numerical basis set and the hybrid Becke, three-parameter Lee–Yang–Parr (B3LYP) functional employed with a Gaussian basis set. The sign and relative strength of the exchange coupling constants calculated with both methods were consistent; as expected, the values calculated with the PBE functional were slightly overestimated, as corroborated by comparison with the experimental magnetic susceptibility curve. Both methods gave a ground spin configuration of S = 3/2 for the Mn7 moiety, which was weakly antiferromagnetically coupled with the other Mn7 fragment, leading to an S = 0 ground spin configuration for the entire Mn14 complex.

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