How H-Bonding Affects Aromaticity of the Ring in Variously Substituted Phenol Complexes with Bases. 4. Molecular Geometry as a Source of Chemical Information

2004 ◽  
Vol 44 (6) ◽  
pp. 2077-2082 ◽  
Author(s):  
Tadeusz M. Krygowski ◽  
Halina Szatyłowicz ◽  
Joanna E. Zachara
Keyword(s):  
Molecular Geometry ◽  
Chemical Information

Solution of organic crystal structures from powder diffraction by combining simulated annealing and direct methods

2003 ◽  
Vol 36 (2) ◽  
pp. 230-238 ◽  
Author(s):  
Angela Altomare ◽  
Rocco Caliandro ◽  
Carmelo Giacovazzo ◽  
Anna Grazia Giuseppina Moliterni ◽  
Rosanna Rizzi
Keyword(s):  
Monte Carlo ◽  
Simulated Annealing ◽  
Electron Density ◽  
Powder Diffraction ◽  
Direct Methods ◽  
Molecular Geometry ◽  
Molecular Structures ◽  
Chemical Information ◽  
Density Map ◽  
Electron Density Map

Theab initiocrystal structure solution from powder diffraction data can be attemptedviadirect methods. If heavy atoms are present, they are usually correctly located; then some crystal chemical information can be exploited to complete the partial structure model. Organic structures are more resistant to direct methods; as an alternative, their molecular geometry is used as prior information for Monte Carlo methods. In this paper, a new procedure is described which combines the information contained in the electron density map provided by direct methods with a Monte Carlo method which uses simulated annealing as a minimization algorithm. A figure of merit has been designed based on the agreement between the experimental and calculated profiles, and on the positions of the peaks in the electron density map. The procedure is completely automatic and has been included inEXPO; its performance has been validated and tested for a set of known molecular structures.

COMPLETE SPACE QUANTUM CHEMISTRY BY MULTIRESOLUTION MULTIWAVELET BASIS SET

2013 ◽  
Vol 11 (04) ◽  
pp. 1360008 ◽  
Author(s):  
HIDEO SEKINO ◽  
AKIRA MATSUMURA ◽  
YUKINA YOKOI ◽  
TETSUYA KATO
Keyword(s):  
Quantum Chemistry ◽  
Geometry Optimization ◽  
Vibrational Analysis ◽  
Molecular Geometry ◽  
Basis Set ◽  
Basis Sets ◽  
Chemical Information ◽  
Gaussian Basis Sets ◽  
Complete Space ◽  
Complete Basis Set

Quantum chemistry program based on Multiresolution Multiwavelet (MRMW) basis set is much simpler and can be more efficient than the conventional one based on Gaussian basis set in molecular geometry optimization because the Hellmann Fynman Theorem (HFT) holds for the complete space which MRMW provides. It is numerically shown that large Gaussian basis sets can provide the chemical information with chemical accuracy for very small molecular systems despite the incompleteness of their basis set. However, even for the relatively small size molecule of CH4 , the error from the basis set incompleteness results in an error larger than an acceptable chemical accuracy. The advantage of the MRMW complete basis set in vibrational analysis is also discussed.

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