Heat capacity of sodium silicate glasses: comparison of experiments with computer simulations

The vibrational density of states (VDOS) and the heat capacities of amorphous SiO(2) and several (Na(2)O)(x)(SiO(2))(1-x), x = 0.2, 0.333, 0.5, silicate glasses have been calculated using computer models generated by molecular dynamics and the reverse Monte Carlo method. Significant changes in the VDOS upon addition of Na2O are predicted. Comparison with experimental data and previous calculations shows that the heat capacity is sensitive mainly to the strength of the Na-O and Si-O pair interactions but not to the medium-range order and the preparation history of the models. It is demonstrated that the increase of the specific heat with increasing alkali oxide for T > 30 K is due to an increase of the Na and non-bridging oxygen partial heat capacities.