Elastic anomalies of anorthite: Molecular dynamics simulations

We investigated the elastic anomalies of anorthite using molecular dynamics simulations in which the temperature and pressure induced P1¯/I1¯ phase transitions were reproduced. The resulting changes in structure were investigated as functions of pressure and temperature. It was found that the temperature-induced elastic anomaly is caused by two different thermal expansion behaviors of atomic motion, that is, increased distance between nearest neighbor atoms and increased Si–O–Al angle. Furthermore, the pressure-induced elastic anomaly was found to be caused by a decrease in the Si–O–Al angle in six-membered rings, which is similar to the cases of vitreous silica or acidic silicate liquids.