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Structure And Stability Of Hexacoordinated Sila Dianions, Mark S. Gordon, Marshall T. Carroll, Larry P. Davis, Larry W. Burggraf
Structure And Stability Of Hexacoordinated Sila Dianions, Mark S. Gordon, Marshall T. Carroll, Larry P. Davis, Larry W. Burggraf
Mark S. Gordon
The structures and stabilities of hexacoordinated silicon-containing dianions SiX6 2- have been investigated by using both ab initio (X= H, F) and semiempirical AMI (X= H, F, OH, Me, Cl) calculations. Both methods predict the hexacoordinated structures to be minima on the potential energy surfaces, although the semiempirical barriers for the reactions SiX6 2- -+ Six5- + x- appear to be rather overestimated based on the ab initio results for X = H, F. The positive charge on the central silicon atom actually increases as the number of ligands increases, and the role of d orbitals on that atom appears …
Theoretical Study Of Pseudorotation Of Pentacoordinated Silicon Anions: The Prototypical Sih5-, Mark S. Gordon, Theresa L. Windus, Larry W. Burggraf, Larry P. Davis
Theoretical Study Of Pseudorotation Of Pentacoordinated Silicon Anions: The Prototypical Sih5-, Mark S. Gordon, Theresa L. Windus, Larry W. Burggraf, Larry P. Davis
Mark S. Gordon
Ab initio and semiempirical calculations are used to analyze the minimum energy path for the pseudorotation of SiH5-. Both AMI and MP2/6-31++G(d,p) predict pseudorotation barriers of 2.4 kcal/mol. A decomposition of the projected vibrational frequencies along the path is used to assist in the interpretation of the process.
Coincidence Orientations Of Crystals In Tetragonal Systems, With Applications To Yba2cu3o7, Abha Singh, N. Chandrasekhar, Alexander H. King
Coincidence Orientations Of Crystals In Tetragonal Systems, With Applications To Yba2cu3o7, Abha Singh, N. Chandrasekhar, Alexander H. King
Alexander H. King
We have developed a method for the characterization of coincidence-site lattices (CSL's) in tetragonal or near-tetragonal orthorhombic structures, by suitable modifications to the method of Grimmer & Warrington [Acta Cryst. (1987), A43, 232-243]. We have applied our method to determine coincidence rotations and the associated information appropriate for forming constrained CSL's in the high-To superconductor YBazCu307-n. The unit cell is orthorhombic with lattice parameters a = 3.82, b = 3"89 and c = 11.67 A for the nominal composition. We present tables of coincidence rotation angles, .Z, CSL, DSCL and associated step vectors up to ,~ = 50. We find …