| Because of its free sintering, high-performance, low cost, and simple preparation, geopolymer has received more and more attention. Geopolymers, arealka linealumino-silicate compounds, which can be nominally represented as nM2O.Al2O3.xSiO2.yH2O. It is observed that the hydrolysis of aluminate andsilicate materials in alkaline solutions results in monomeric [Al(OH)4]–, [SiO2(OH)2]2– and [SiO(OH)3]– species, respectively.Along with the quickly improved computation theory and method in recent years, the Density Functional Theory (DFT) has achieved a rapid progress, and it has been used to explore solid-state systems. In this work, systematic calculations of the polymerization mechanisms of geopolymers have been carried out using DMOL3 based on the DFT theory.The transition state structure of [Si2(OH)4O3]2- formed from two [SiO2(OH)2]2– groups is optimized. The results demonstrate that a hydroxyl lost from one [SiO(OH)3]– forms a water molecule with a hydrogen atom lost from the other [SiO(OH)3]– and this is the only transition state in the condensation of [Si2(OH)4O3]2-. An energy of 0.0263eV is consumed and a relative long time is required in the structure optimization.The optimization of the transition state structure of [SiAl(OH)5O2]2- from [Al(OH)4]– and [SiO2(OH)2]2– groups indicates that a hydroxyl lost from [SiO(OH)3]– forms a water molecule with a hydrogen atom lost from [Al(OH)4]–, and this is the only transition state in the condensation of [SiAl(OH)5O2]2-. A much lower energy of 0.0082eV is consumed in the structure optimization and also the optimization takes a much shorter time as compared with the case of [Si2(OH)4O3]2-.It is clear that the reaction of [SiAl(OH)5O2]2- in the geopolymer is much faster than that of [Si2(OH)4O3]2- in the common cement, implying that the rate of hardening is much faster for the geopolymer than for the common cement. These results are well consistent with the available observations. Undoubtedly, the present study is of importance in the development of geopolymeric materials.
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