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Using molecular dynamics computer simulations we investigate how in silicathe glass transition and the properties of the resulting glass depend on thecooling rate with which the sample is cooled. By coupling the system to a heatbath with temperature $T_b(t)$, we cool the system linearly in time,$T(t)=T_i-\gamma t$, where $\gamma$ is the cooling rate. We find that the glasstransition temperature $T_g$ is in accordance with a logarithmic dependence onthe cooling rate. In qualitative accordance with experiments, the density showsa local maximum, which becomes more pronounced with decreasing cooling rate.The enthalpy, density and the thermal expansion coefficient for the glass atzero temperature decrease with decreasing $\gamma$. We show that alsomicroscopic quantities, such as the radial distribution function, the bond-bondangle distribution function, the coordination numbers and the distributionfunction for the size of the rings depend significantly on $\gamma$. Wedemonstrate that the cooling rate dependence of these microscopic quantities issignificantly more pronounced than the one of macroscopic properties.Furthermore we show that these microscopic quantities, as determined from oursimulation, are in good agreement with the ones measured in real experiments,thus demonstrating that the used potential is a good model for silica glass.The vibrational spectrum of the system also shows a significant dependence onthe cooling rate and is in qualitative accordance with the one found inexperiments. Finally we investigate the properties of the system at finitetemperatures in order to understand the microscopic mechanism for the densityanomaly. We show that the anomaly is related to a densification and subsequentopening of the tetrahedral network when the temperature is decreased, whereasComment: Figures are available from W. Ko

Cooling-rate effects in amorphous silica: A computer-simulation study