| Aim: To asses from first principles if Dietzels' theorem holds. Methods: Experiments to date on alkali disilicate systems suggest that Dietzels' theorem is valid in silicate systems and profoundly affects the alkali exchange in minerals. To underpin these experimental observations we have embarked on a theoretical study. R2O(R=H, Li, Na, K, Rb, Cs) molecules have been selected and their stability is in the process of being calculated to estimate two effects. The first one pertains to the exhange of a large alkali atom by a small one in these molecules which according to Dietzel's theorem results in a alkali-oxygen bondlengthening for the large alkali and a contraction for the small one. The second one deals with the exchange energies involved for the diadochy of two alkalis whith similar cationic field strength. This exchange will not occur according to Dietzel's theorem. The calculations are carried out using various levels of ab initio quantum mechanical calculations. |
