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Minimum Structures (minimum + structure)

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Chemistry100%

Selected Abstracts

ChemInform Abstract: Ab initio Search for Global Minimum Structures of the Novel B3Hy (y-= 4,7) Neutral and Anionic Clusters.

CHEMINFORM, Issue 51 2009
Jared K. Olson
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Density functional and ab initio studies on structures and energies of the ground state of CrCO

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2007
Joonghan Kim
Abstract CrCO was studied using density functional theory (DFT) and ab initio methods. We obtained the two-dimensional potential energy surface (PES), geometry, and vibrational frequencies for CrCO in a septet state. Two minimum structures were found in the CCSD(T) calculation, including a local minimum that is a weak van der Waals (vdW) complex. All DFT methods yield only one minimum structure. We demonstrate that the bond dissociation energy (0.50 kcal/mol) and vibrational frequency (1981.1 cm,1) of CrCO calculated using CCSD(T) are in better agreement with experimental values (<1.5 kcal/mol and 1977 cm,1) than any of the reported theoretical studies. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source]

Electrophilic Attack on Sulfur,Sulfur Bonds: Coordination of Lithium Cations to Sulfur-Rich Molecules Studied by Ab Initio MO Methods

CHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2005
Yana Steudel Dr.
Abstract Complex formation between gaseous Li+ ions and sulfur-containing neutral ligands, such as H2S, Me2Sn (n = 1,5; Me = CH3) and various isomers of hexasulfur (S6), has been studied by ab initio MO calculations at the G3X(MP2) level of theory. Generally, the formation of LiSn heterocycles and clusters is preferred in these reactions. The binding energies of the cation in the 29 complexes investigated range from ,88 kJ,mol,1 for [H2SLi]+ to ,189 kJ,mol,1 for the most stable isomer of [Me2S5Li]+ which contains three-coordinate Li+. Of the various S6 ligands (chair, boat, prism, branched ring, and triplet chain structures), two isomeric complexes containing the S5S ligand have the highest binding energies (,163±1 kJ,mol,1). However, the global minimum structure of [LiS6]+ is of C3v symmetry with the six-membered S6 homocycle in the well-known chair conformation and three LiS bonds with a length of 256 pm (binding energy: ,134 kJ,mol,1). Relatively unstable isomers of S6 are stabilized by complex formation with Li+. The interaction between the cation and the S6 ligands is mainly attributed to ion,dipole attraction with a little charge transfer, except in cations containing the six sulfur atoms in the form of separated neutral S2, S3, or S4 units, as in [Li(S3)2]+ and [Li(S2)(S4)]+. In the two most stable isomers of the [LiS6]+ complexes, the number of SS bonds is at maximum and the coordination number of Li+ is either 3 or 4. A topological analysis of all investigated complexes revealed that the LiS bonds of lengths below 280 pm are characterized by a maximum electron-density path and closed-shell interaction. [source]

Density functional and ab initio studies on structures and energies of the ground state of CrCO

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2007
Joonghan Kim
Abstract CrCO was studied using density functional theory (DFT) and ab initio methods. We obtained the two-dimensional potential energy surface (PES), geometry, and vibrational frequencies for CrCO in a septet state. Two minimum structures were found in the CCSD(T) calculation, including a local minimum that is a weak van der Waals (vdW) complex. All DFT methods yield only one minimum structure. We demonstrate that the bond dissociation energy (0.50 kcal/mol) and vibrational frequency (1981.1 cm,1) of CrCO calculated using CCSD(T) are in better agreement with experimental values (<1.5 kcal/mol and 1977 cm,1) than any of the reported theoretical studies. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source]

Conformational analysis of arginine in gas phase,A strategy for scanning the potential energy surface effectively

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 3 2008
Sebastian Schlund
Abstract The determination of all possible low-lying energy conformers of flexible molecules is of fundamental interest for various applications. It necessitates a reliable conformational search that is able to detect all important minimum structures and calculates the energies on an adequate level of theory. This work presents a strategy to identify low-energy conformers using arginine as an example by means of a force-field based conformational search in combination with high-level geometry optimizations (RI-MP2/TZVPP+). The methods used for various stages in the conformational search strategy are shown and various pitfalls are discussed. We can show that electronic energies calculated on a DFT level of theory with standard exchange-correlation functionals strongly underestimate the intramolecular stabilization resulting from stacked orientations of the guanidine and carbonyl moiety of arginine due to the deficiency of DFT to describe dispersion effects. In this case by usage of electron correlation methods, low energy conformers comprising stacked arrangements that are counterintuitive become favorable. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2008 [source]

Structures and Vibrational Spectra of the Sulfur-Rich Oxides SnO (n = 4,9): The Importance of ,*,,* Interactions

CHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2007
Wah Wong Prof.
Abstract The structures of a large number of isomers of the sulfur oxides SnO with n = 4,9 have been calculated at the G3X(MP2) level of theory. In most cases, homocyclic molecules with exocyclic oxygen atoms in an axial position are the global minimum structures. Perfect agreement is obtained with experimentally determined structures of S7O and S8O. The most stable S4O isomer as well as some less stable isomers of S5O and S6O are characterized by a strong ,*,,* interaction between SO and SS groups, which results in relatively long SS bonds with internuclear distances of 244,262,pm. Heterocyclic isomers are less stable than the global minimum structures, and this energy difference approximately increases with the ring size: 17 (S4O), 40 (S5O), 32 (S6O), 28 (S7O), 45 (S8O), and 54,kJ,mol,1 (S9O). Owing to a favorable ,*,,* interaction, preference for an axial (or endo) conformation is calculated for the global energy minima of S7O, S8O, and S9O. Vapor-phase decomposition of SnO molecules to SO2 and S8 is strongly exothermic, whereas the formation of S2O and S8 is exothermic if n<7, but slightly endothermic for S7O, S8O, and S9O. The calculated vibrational spectra of the most stable isomers of S6O, S7O, and S8O are in excellent agreement with the observed data. [source]