  Establishing the composition-structure-property relationships for amorphous
materials is critical for many important natural and engineering processes,
including the dissolution of highly complex volcanic glasses. In this
investigation, we performed force field molecular dynamics (MD) simulations to
generate detailed structural representations for ten natural
CaO-MgO-Al2O3-SiO2-TiO2-FeO-Fe2O3-Na2O-K2O glasses with compositions ranging
from rhyolitic to basaltic. Based on the resulting atomic structural
representations at 300 K, we have calculated the partial radial distribution
functions, nearest interatomic distances and coordination number, which are
consistent with the literature data on silicate-based glasses. Based on these
structural attributes and classical bond valence models, we have introduced a
novel structural descriptor, i.e., average metal-oxygen (M-O) bond strength
parameter, which has captured the log dissolution rates of the ten glasses at
both acidic and basic conditions (based on literature data) with R2 values of
~0.80-0.92 based on linear regression. This structural descriptor is seen to
outperform several other structural descriptors also derived from MD simulation
results, including the average metal oxide dissociation energy, the average
self-diffusion coefficient of all the atoms at their melting points, and the
energy barrier of self-diffusion. Furthermore, we showed that the MD-derived
descriptors generally exhibit better predictive performance than the degree of
depolymerization parameter commonly used to describe glass and mineral
reactivity. The results suggest that the structural descriptors derived from MD
simulations, especially the average M-O bond strength parameter, are promising
structural descriptors for connecting composition with dissolution rates of
highly complex natural glasses.
