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M B Boisen - One of the best experts on this subject based on the ideXlab platform.
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Patai's Chemistry of Functional Groups - A Molecular Modeling of the Bonded Interactions of Crystalline Silica
PATAI'S Chemistry of Functional Groups, 2009Co-Authors: G V Gibbs, M B BoisenAbstract:1 Introduction 2 Bond Length–Bond Strength Variations in Silicates and Related Molecules 3 A Potential Energy Surface for the SiOSi Skeleton of the Disilicic Acid Molecule 4 Bond Critical Point Properties of the Electron Density Distribution of the Skeletal SiOSi Unit 5 A Reproduction of the Structures and Related Properties of the Known Silica Polymorphs 6 A Generation of New Structure Types for Silica 7 Concluding Remarks 8 Acknowledgments Keywords: silicate bonded interactions; molecular modeling of crystalline silica bonded interactions; resonance bond numbers; Disilicic Acid H6Si2O7 molecule geometry; electron density distribution of crystal and bond critical point; minimum energy SiO bond length; silica polymorphs SiO bond length and SiOSi angle variations; generation new silica structure types
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a generation of framework structures for the tectosilicates using a molecular based potential energy function and simulated annealing strategies
Microporous and Mesoporous Materials, 1999Co-Authors: M B Boisen, G V Gibbs, Michael Okeeffe, K L BartelmehsAbstract:Abstract More than 1400 framework model structures have been derived using simulated annealing strategies and the geometry and a potential energy function calculated for the Disilicic Acid molecule. The derivation was undertaken starting with either 3 or 6 formula units of SiO 2 randomly distributed in a unit cell of variable geometry and P 1 space group symmetry. More than 40 model low energy structures are described, including quartz and a mixed stacking sequences of tridymite and cristobalite. As observed in earlier calculations with 4 formula units per unit cell, the tridymite topology was not generated. In addition to model structures that match or relate to the framework structures of the zeolites NaJ, bikitaite, sodalite and cancrinite, model structures with Si networks were derived that match those enumerated by Smith [J.V. Smith, Am. Min. 62 (1977) 703] and O'Keeffe and Brese [M. O'Keeffe, N.E. Brese, Acta Cryst. A48 (1992) 663]. A number of the model structures are apparently new and have yet to be described and cataloged. The successful derivation of the known structure types of silica and the framework models of known tectosilicates using molecular models, indicate that the forces that govern the structure of silica behave as if short ranged.
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Framework silica structures generated using simulated annealing with a potential energy function based on an H_6Si_2O_7 molecule
Physics and Chemistry of Minerals, 1994Co-Authors: M B Boisen, G V Gibbs, M. S. T. BukowinskiAbstract:A simulated annealing technique was used to search for global and local minimum energy structures of a potential energy model for silica. The model is based on ab initio SCF MO calculations on the Disilicic Acid molecule, H_6Si_2O_7. Starting with 4 SiO_2 units, with the atoms randomly distributed in the unit cell, 23 distinct silica tetrahedral framework structures were found, with a variety of space group symmetries and cell dimensions. Despite the assumption of P 1 space group symmetry for the starting structure, only 7 of the local minimum energy structures were found to possess triclinic symmetry with the remainder exhibiting symmetries ranging from P c to $$I\bar 42d$$ to within 0.001 Å. Although the interaction potential for the Disilicic Acid molecule has a single minimum energy SiO bond length and SiOSi angle, the local minimum energy structures exhibit angles that range between 105° and 180° and bond lengths that range between 1.55 and 1.68 Å. The correlation observed for coesite and the other silica polymorphs between SiO bond length and f_s(O) is reproduced. The generated structures show a wide variety of coordination sequences, ring sizes and framework densities, the later ranging from 19.8 to 35.5 Si/1000 Å^3. The energies of these structures correlate with their framework densities, particularly for higher energy structures.
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framework silica structures generated using simulated annealing with a potential energy function based on an h6si2o7 molecule
Physics and Chemistry of Minerals, 1994Co-Authors: M B Boisen, G V Gibbs, M. S. T. BukowinskiAbstract:A simulated annealing technique was used to search for global and local minimum energy structures of a potential energy model for silica. The model is based on ab initio SCF MO calculations on the Disilicic Acid molecule, H6Si2O7. Starting with 4 SiO2 units, with the atoms randomly distributed in the unit cell, 23 distinct silica tetrahedral framework structures were found, with a variety of space group symmetries and cell dimensions. Despite the assumption of P 1 space group symmetry for the starting structure, only 7 of the local minimum energy structures were found to possess triclinic symmetry with the remainder exhibiting symmetries ranging from P c to $$I\bar 42d$$ to within 0.001 A. Although the interaction potential for the Disilicic Acid molecule has a single minimum energy SiO bond length and SiOSi angle, the local minimum energy structures exhibit angles that range between 105° and 180° and bond lengths that range between 1.55 and 1.68 A. The correlation observed for coesite and the other silica polymorphs between SiO bond length and fs(O) is reproduced. The generated structures show a wide variety of coordination sequences, ring sizes and framework densities, the later ranging from 19.8 to 35.5 Si/1000 A3. The energies of these structures correlate with their framework densities, particularly for higher energy structures.
G V Gibbs - One of the best experts on this subject based on the ideXlab platform.
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Patai's Chemistry of Functional Groups - A Molecular Modeling of the Bonded Interactions of Crystalline Silica
PATAI'S Chemistry of Functional Groups, 2009Co-Authors: G V Gibbs, M B BoisenAbstract:1 Introduction 2 Bond Length–Bond Strength Variations in Silicates and Related Molecules 3 A Potential Energy Surface for the SiOSi Skeleton of the Disilicic Acid Molecule 4 Bond Critical Point Properties of the Electron Density Distribution of the Skeletal SiOSi Unit 5 A Reproduction of the Structures and Related Properties of the Known Silica Polymorphs 6 A Generation of New Structure Types for Silica 7 Concluding Remarks 8 Acknowledgments Keywords: silicate bonded interactions; molecular modeling of crystalline silica bonded interactions; resonance bond numbers; Disilicic Acid H6Si2O7 molecule geometry; electron density distribution of crystal and bond critical point; minimum energy SiO bond length; silica polymorphs SiO bond length and SiOSi angle variations; generation new silica structure types
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a generation of framework structures for the tectosilicates using a molecular based potential energy function and simulated annealing strategies
Microporous and Mesoporous Materials, 1999Co-Authors: M B Boisen, G V Gibbs, Michael Okeeffe, K L BartelmehsAbstract:Abstract More than 1400 framework model structures have been derived using simulated annealing strategies and the geometry and a potential energy function calculated for the Disilicic Acid molecule. The derivation was undertaken starting with either 3 or 6 formula units of SiO 2 randomly distributed in a unit cell of variable geometry and P 1 space group symmetry. More than 40 model low energy structures are described, including quartz and a mixed stacking sequences of tridymite and cristobalite. As observed in earlier calculations with 4 formula units per unit cell, the tridymite topology was not generated. In addition to model structures that match or relate to the framework structures of the zeolites NaJ, bikitaite, sodalite and cancrinite, model structures with Si networks were derived that match those enumerated by Smith [J.V. Smith, Am. Min. 62 (1977) 703] and O'Keeffe and Brese [M. O'Keeffe, N.E. Brese, Acta Cryst. A48 (1992) 663]. A number of the model structures are apparently new and have yet to be described and cataloged. The successful derivation of the known structure types of silica and the framework models of known tectosilicates using molecular models, indicate that the forces that govern the structure of silica behave as if short ranged.
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Framework silica structures generated using simulated annealing with a potential energy function based on an H_6Si_2O_7 molecule
Physics and Chemistry of Minerals, 1994Co-Authors: M B Boisen, G V Gibbs, M. S. T. BukowinskiAbstract:A simulated annealing technique was used to search for global and local minimum energy structures of a potential energy model for silica. The model is based on ab initio SCF MO calculations on the Disilicic Acid molecule, H_6Si_2O_7. Starting with 4 SiO_2 units, with the atoms randomly distributed in the unit cell, 23 distinct silica tetrahedral framework structures were found, with a variety of space group symmetries and cell dimensions. Despite the assumption of P 1 space group symmetry for the starting structure, only 7 of the local minimum energy structures were found to possess triclinic symmetry with the remainder exhibiting symmetries ranging from P c to $$I\bar 42d$$ to within 0.001 Å. Although the interaction potential for the Disilicic Acid molecule has a single minimum energy SiO bond length and SiOSi angle, the local minimum energy structures exhibit angles that range between 105° and 180° and bond lengths that range between 1.55 and 1.68 Å. The correlation observed for coesite and the other silica polymorphs between SiO bond length and f_s(O) is reproduced. The generated structures show a wide variety of coordination sequences, ring sizes and framework densities, the later ranging from 19.8 to 35.5 Si/1000 Å^3. The energies of these structures correlate with their framework densities, particularly for higher energy structures.
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framework silica structures generated using simulated annealing with a potential energy function based on an h6si2o7 molecule
Physics and Chemistry of Minerals, 1994Co-Authors: M B Boisen, G V Gibbs, M. S. T. BukowinskiAbstract:A simulated annealing technique was used to search for global and local minimum energy structures of a potential energy model for silica. The model is based on ab initio SCF MO calculations on the Disilicic Acid molecule, H6Si2O7. Starting with 4 SiO2 units, with the atoms randomly distributed in the unit cell, 23 distinct silica tetrahedral framework structures were found, with a variety of space group symmetries and cell dimensions. Despite the assumption of P 1 space group symmetry for the starting structure, only 7 of the local minimum energy structures were found to possess triclinic symmetry with the remainder exhibiting symmetries ranging from P c to $$I\bar 42d$$ to within 0.001 A. Although the interaction potential for the Disilicic Acid molecule has a single minimum energy SiO bond length and SiOSi angle, the local minimum energy structures exhibit angles that range between 105° and 180° and bond lengths that range between 1.55 and 1.68 A. The correlation observed for coesite and the other silica polymorphs between SiO bond length and fs(O) is reproduced. The generated structures show a wide variety of coordination sequences, ring sizes and framework densities, the later ranging from 19.8 to 35.5 Si/1000 A3. The energies of these structures correlate with their framework densities, particularly for higher energy structures.
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quantum mechanical hartree fock potential surfaces and calculations on minerals
Pacific Rim Conference on Multimedia, 1991Co-Authors: Antonio C Lasaga, G V GibbsAbstract:Extensive ab initio results using the robust 6-31G* basis set are compared with earlier STO-3G calculations on the Si-O-H system. The 6-31G* results clearly show that improving the quality of the ab initio calculations increases the accuracy of the bonding description within the monosilicic and Disilicic Acid molecules. In turn, the new ab initio results predict quite well the dynamics of the SiO bonds in framework silicates such as quartz or silica glass.
Konstantinos D. Demadis - One of the best experts on this subject based on the ideXlab platform.
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Bioinspired insights into silicic Acid stabilization mechanisms: the dominant role of polyethylene glycol-induced hydrogen bonding.
Journal of the American Chemical Society, 2014Co-Authors: Melina Preari, Katrin Spinde, Joëlle Lazic, Eike Brunner, Konstantinos D. DemadisAbstract:Mono- and Disilicic Acids were stabilized by uncharged polyethylene glycols (PEGs) in silica-supersaturated solutions (the starting solution contained 500 ppm/8.3 mM sodium orthosilicate, Na2SiO3·5H2O, expressed as SiO2) at pH = 7, most likely by hydrogen bonding between the silanol groups and −CH2–CH2–O–ether moieties. The stabilization was monitored by measuring molybdate-reactive silica and also by a combination of liquid- and solid-state 29Si NMR spectroscopy. It depends on PEG concentration (20–100 ppm) and molecular weight (1550–20 000 Da). Two narrow 29Si NMR signals characteristic for monosilicic Acid (Q0) and Disilicic Acid (Q1) can be observed in 29Si NMR spectra of solutions containing PEG 10000 with intensities distinctly higher than the control, that is, in the absence of PEG. Silica-containing precipitates are observed in the presence of PEG, in contrast to the gel formed in the absence of PEG. These precipitates exhibit similar degrees of silica polycondensation as found in the gel as can b...
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Influence of Polyamines and Related Macromolecules on Silicic Acid Polycondensation: Relevance to “Soluble Silicon Pools”?
Chemistry of Materials, 2011Co-Authors: Katrin Spinde, Eike Brunner, Konstantinos Pachis, Ioanna Antonakaki, Silvia Paasch, Konstantinos D. DemadisAbstract:The influence of a number of N-containing macromolecules on the polycondensation of silicic Acid to form amorphous silica is studied by the combined use of 29Si NMR spectroscopy and the silicomolybdate test. Polymeric additives include poly(allylamine hydrochloride) (PAH), the poly(aminoamide) dendrimer of generation 1 (PAMAM-1), poly(ethyleneimine) (PEI), and poly(vinylpyrrolidone) (PVP). These studies were performed under biologically relevant conditions (pH 5.4 and 7.0) using aqueous solutions of isotope-labeled sodium [29Si]metasilicate as the precursor compound. It was found at pH 5.4 that all additives accelerate silicic Acid polycondensation, except for PVP, which exerts a minor silicic Acid stabilizing effect. At pH 7.0, polycondensation is much faster in the presence of PAMAM-1, PEI, and PAH. However, PVP significantly stabilizes mono- and Disilicic Acid. Silica precipitates were also studied by 29Si NMR spectroscopy. The effect observed for PVP is striking and indicates that the silicic Acid pol...
K L Bartelmehs - One of the best experts on this subject based on the ideXlab platform.
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a generation of framework structures for the tectosilicates using a molecular based potential energy function and simulated annealing strategies
Microporous and Mesoporous Materials, 1999Co-Authors: M B Boisen, G V Gibbs, Michael Okeeffe, K L BartelmehsAbstract:Abstract More than 1400 framework model structures have been derived using simulated annealing strategies and the geometry and a potential energy function calculated for the Disilicic Acid molecule. The derivation was undertaken starting with either 3 or 6 formula units of SiO 2 randomly distributed in a unit cell of variable geometry and P 1 space group symmetry. More than 40 model low energy structures are described, including quartz and a mixed stacking sequences of tridymite and cristobalite. As observed in earlier calculations with 4 formula units per unit cell, the tridymite topology was not generated. In addition to model structures that match or relate to the framework structures of the zeolites NaJ, bikitaite, sodalite and cancrinite, model structures with Si networks were derived that match those enumerated by Smith [J.V. Smith, Am. Min. 62 (1977) 703] and O'Keeffe and Brese [M. O'Keeffe, N.E. Brese, Acta Cryst. A48 (1992) 663]. A number of the model structures are apparently new and have yet to be described and cataloged. The successful derivation of the known structure types of silica and the framework models of known tectosilicates using molecular models, indicate that the forces that govern the structure of silica behave as if short ranged.
Katrin Spinde - One of the best experts on this subject based on the ideXlab platform.
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Bioinspired insights into silicic Acid stabilization mechanisms: the dominant role of polyethylene glycol-induced hydrogen bonding.
Journal of the American Chemical Society, 2014Co-Authors: Melina Preari, Katrin Spinde, Joëlle Lazic, Eike Brunner, Konstantinos D. DemadisAbstract:Mono- and Disilicic Acids were stabilized by uncharged polyethylene glycols (PEGs) in silica-supersaturated solutions (the starting solution contained 500 ppm/8.3 mM sodium orthosilicate, Na2SiO3·5H2O, expressed as SiO2) at pH = 7, most likely by hydrogen bonding between the silanol groups and −CH2–CH2–O–ether moieties. The stabilization was monitored by measuring molybdate-reactive silica and also by a combination of liquid- and solid-state 29Si NMR spectroscopy. It depends on PEG concentration (20–100 ppm) and molecular weight (1550–20 000 Da). Two narrow 29Si NMR signals characteristic for monosilicic Acid (Q0) and Disilicic Acid (Q1) can be observed in 29Si NMR spectra of solutions containing PEG 10000 with intensities distinctly higher than the control, that is, in the absence of PEG. Silica-containing precipitates are observed in the presence of PEG, in contrast to the gel formed in the absence of PEG. These precipitates exhibit similar degrees of silica polycondensation as found in the gel as can b...
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Influence of Polyamines and Related Macromolecules on Silicic Acid Polycondensation: Relevance to “Soluble Silicon Pools”?
Chemistry of Materials, 2011Co-Authors: Katrin Spinde, Eike Brunner, Konstantinos Pachis, Ioanna Antonakaki, Silvia Paasch, Konstantinos D. DemadisAbstract:The influence of a number of N-containing macromolecules on the polycondensation of silicic Acid to form amorphous silica is studied by the combined use of 29Si NMR spectroscopy and the silicomolybdate test. Polymeric additives include poly(allylamine hydrochloride) (PAH), the poly(aminoamide) dendrimer of generation 1 (PAMAM-1), poly(ethyleneimine) (PEI), and poly(vinylpyrrolidone) (PVP). These studies were performed under biologically relevant conditions (pH 5.4 and 7.0) using aqueous solutions of isotope-labeled sodium [29Si]metasilicate as the precursor compound. It was found at pH 5.4 that all additives accelerate silicic Acid polycondensation, except for PVP, which exerts a minor silicic Acid stabilizing effect. At pH 7.0, polycondensation is much faster in the presence of PAMAM-1, PEI, and PAH. However, PVP significantly stabilizes mono- and Disilicic Acid. Silica precipitates were also studied by 29Si NMR spectroscopy. The effect observed for PVP is striking and indicates that the silicic Acid pol...