Ab initio studies of the protonation of CO, N2 and NO+: Calculation of the minimum energy reaction paths

1978 ◽  
Vol 47 (3) ◽  
pp. 223-231 ◽  
Author(s):  
Neena L. Summers ◽  
James Tyrrell
Keyword(s):  
Ab Initio ◽  
Minimum Energy ◽  
Reaction Paths ◽  
Energy Reaction

scholarly journals An ab initio Hartree-Fock Investigation of Endohedral Sc@C82

1998 ◽  
Vol 53 (9) ◽  
pp. 801-805 ◽  
Author(s):  
Andrea Gruß ◽  
Michael C. Böhm ◽  
Joachim Schulte ◽  
Klaus-Peter Dinse
Keyword(s):  
Ab Initio ◽  
Minimum Energy ◽  
Fullerene Cage ◽  
Site Symmetry ◽  
Fold Axis ◽  
Hartree Fock ◽  
Endohedral Complex ◽  
Experimental Findings ◽  
Ab Initio Hf ◽  
Hf Calculations

Abstract The electronic structure of endohedral Sc@C82 with a C82 cage of C2v symmetry has been studied by ab initio Hartree-Fock (HF) calculations. The optimized position of Sc in the configuration of minimum energy is predicted to be on the two-fold axis of the fullerene cage. In the corresponding configuration Sc is above the center of a hexagon of site symmetry C2 . This structure of C2v symmetry is nearly degenerate with Cs and Ct structures with Sc slightly displaced from the center of the coordinated hexagon. The binding energy of the endohedral complex is larger than 3.55 eV. The ab initio HF data of the C2v topoisomer of the fullerene unit are compared with new experimental findings and HF results derived for the 3(C2) topoisomer of the C82 cage.

scholarly journals Geometrical parameterization of the crystal chemistry of P63/m apatites: comparison with experimental data and ab initio results

2005 ◽  
Vol 61 (6) ◽  
pp. 635-655 ◽  
Author(s):  
Patrick H. J. Mercier ◽  
Yvon Le Page ◽  
Pamela S. Whitfield ◽  
Lyndon D. Mitchell ◽  
Isobel J. Davidson ◽  
...  
Keyword(s):  
Single Crystal ◽  
Ab Initio ◽  
Minimum Energy ◽  
Structure Type ◽  
Chemical Model ◽  
Crystal Chemical ◽  
Chemical Parameters ◽  
Rietveld Refinements ◽  
Cell Parameters ◽  
Cell Data

Experimental structure refinements and ab initio simulation results for 18 published, fully ordered P63/m (A^{\rm I}_4)(A^{\rm II}_6)(BO4)6 X 2 apatite end-member compositions have been analyzed in terms of a geometric crystal-chemical model that allows the prediction of unit-cell parameters (a and c) and all atom coordinates. To an accuracy of ± 0.025 Å, the magnitude of c was reproduced from crystal-chemical parameters characterizing chains of …–A II–O3–B–O3–A II–... atoms, whereas that of a was determined from those describing (A IO6)–(BO4) polyhedral arrangements. The c/a ratio could be predicted to ±0.2% using multi-variable functions based on geometric crystal-chemical model predictions, but could not be ascribed to the adjustment of a single crystal-chemical parameter. The correlations observed between algebraically independent crystal-chemical parameters representing the main observed polyhedral distortions reveal them as the minimum-energy solution to accommodate misfit components within this flexible structure type. For materials with given composition, good agreement (within ± 0.5–2.0%) of ab initio crystal-chemical parameters was observed with only those from single-crystal refinements with R ≤ 4.0%. Agreement with single-crystal work with R > 4.0% was not as good, while the scatter with those from Rietveld refinements was considerable. Accordingly, ab initio cell data, atomic coordinates and crystal-chemical parameters were reported here for the following compositions awaiting experimental work: (Zn,Hg)10(PO4)6(Cl,F)2, (Ca,Cd)10(VO4)6Cl2 and (Ca,Pb,Cd)10(CrO4)6Cl2.

Intermolecular Force-Field Parameters for Boron Hydrides

1998 ◽  
Vol 54 (1) ◽  
pp. 41-49 ◽  
Author(s):  
D. E. Williams ◽  
D. Gao
Keyword(s):  
Force Field ◽  
Ab Initio ◽  
Crystal Structures ◽  
Weighted Least Squares ◽  
Minimum Energy ◽  
Structural Parameter ◽  
Exponential Dependence ◽  
Monoclinic Space Group ◽  
Boron Hydrides ◽  
Force Field Parameters

Intermolecular atom–atom force-field parameters of the (exp-6-1) type for B and H atoms in boron hydrides were determined. They were obtained by full-weighted least-squares minimization of 116 forces in 15 observed crystal structures of boranes, the heat of sublimation of B10H14 and data from ab initio wavefunction calculations for diborane. Net atomic charges were obtained by fitting them to molecular electric potentials calculated from ab initio wavefunctions. Charges of terminal hydrogens were usually negative and those of bridging hydrogens usually positive. Repulsion-energy calculations for the B2H6 dimer provided the exponential dependence of H...H repulsion. Using the resulting force field, minimum-energy crystal structures were found with structural parameter values close to those of the observed structures. For diborane, energy minimization beginning with randomly oriented molecules placed initially in an 8 × 8 × 8 body-centered orthogonal cell led to the observed crystal structure and monoclinic space group.

Ab initio study of the minimum-energy structure of trans-azobenzene

2002 ◽  
Vol 360 (3-4) ◽  
pp. 349-354 ◽  
Author(s):  
Noriyuki Kurita ◽  
Tsutomu Ikegami ◽  
Yasuyuki Ishikawa
Keyword(s):  
Ab Initio ◽  
Minimum Energy ◽  
Energy Structure ◽  
Ab Initio Study ◽  
Trans Azobenzene
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