The zwitterion isomer of orthosilicic acid and its role in neutral pH dimerization from density functional theory.

Using density functional theory, the plausible existence of the zwitterion isomer of orthosilicic acid is proposed to account for some of the properties of silica in water. Explicit hydration and explicit addition of salt are used in modeling the zwitterion and the dimerization reaction. Paths between orthosilicic acid, the zwitterion and the autoionization products are presented. The pK for the formation of the aqueous zwitterion species is calculated to be 7.78 in dilute silica solutions and the activation energy for the dimerization reaction ranges from 59.8 kJ/mol to 70.7 kJ/mol depending on salt concentration.