Ab Initio Studies of Silica-Based Clusters. Part I. Energies and Conformations of Simple Clusters

Abstract

To understand the complex mechanisms of reaction, solvation, and diffusion that determine the chemistry of silica in solution, it is necessary to study first the silicate clusters that participate in these processes. We have investigated, by ab initio density functional methods, all silica-based clusters of the form Si x O y (OH) z , with a maximum of five silicon atoms and two intramolecular condensations, plus the six-silicon ring and the eightsilicon containing cube. In this article (part I), we report our results on the structure, charge distribution, and energy of the simpler clusters: the monomer Si(OH) 4 , the dimer Si 2 O(OH) 6 , the linear trimer Si 3 O 2 (OH) 8 , the ring trimer Si 3 O 3 (OH) 6 , the linear tetramer Si 4 O 3 (OH) 10 , the ring tetramer Si 4 O 4 (OH) 8 , the linear pentamer Si 5 O 4 (OH) 12 , and the cubic cage Si 8 O 12 (OH) 8 . We also present density functional results for aluminosilicate clusters: Al(OH) 4 -, Al 2 O(OH) 6 2-, and SiAlO(OH) 6 -. The results for the more complex clusters are presented in the subsequent article (part II). Our studies reveal a wide diversity of structures and consequently of charge distributions and energies for these clusters, that directly influence their chemical behavior, in particular the interaction with other clusters and with the solvent.

Silicate chain formation in the nanostructure of cement-based materials

“…Note that the stability of the silicate chains has not been addressed in previous studies that focused on using either pair potentials 8 or ab initio calculations. 11,12,25,26 In Fig. 5͑b͒, the stability index, S͑m͒, is depicted ͑solid line͒ as a function of m. The local maxima of S͑m͒ happen at m = 2, 5, and 8, showing that these are the most stable configurations in the analyzed range.…”

“…3. For the monomers, two well-known silicate units found in the cementitious environment 1 and in sol-gel alkaline processes, 6,[8][9][10][11][12] Si͑OH͒ 4 and Si͑OH͒ 3 O − , have been chosen. The pentacoordinated species Si͑OH͒ 5 − ͑Refs.…”

Molecular Dynamics Simulation of the Early Stages of the Synthesis of Periodic Mesoporous Silica

“…Unfortunately, we are not aware of any available force field that incorporates reliable parameters for soluble anionic silicates. Pereira et al 48 have developed a force field for soluble neutral silicates based on previous ab initio calculations by Hill and Sauer 49 , and on their own density functional theory (DFT) studies on neutral silicates 50 . Their potential parameters were validated against experimental data for pure, liquid silica alkoxides at several temperatures and pressures 51 .…”

“…Thus, we have adapted the force field of Pereira et al 48 by modifying some parameters according to our own DFT calculations of anionic silicate species 52 . In particular, the angle-bending force constants, the torsional parameters and the L-J parameters were kept unchanged, while the bond lengths and angles were slightly modified in accordance with our recent DFT geometries (obtained using a larger basis set than that in the study of Pereira et al 50 ).…”

Theoretical investigation on the role of mineral dust aerosol in atmospheric reaction: A case of the heterogeneous reaction of formaldehyde with NO 2 onto SiO 2 dust surface

“…This results in a large abundance of SiO 2 in the atmosphere. In the nature, the surface of most SiO 2 powders and gels is made of silanol hydroxyl groups (SiOH), formed by extremely small particles of silica or by porous aggregates (Pereira et al, 1999a). Thus, the natural clay mineral, such as phyllosilicate, is abundant with a large number of siloxane SieOeSi bridges and SiOH on the surface.…”