  Based on molecular dynamics simulations of a lithium metasilicate glass we
study the potential of bond valence sum calculations to identify sites and
diffusion pathways of mobile Li ions in a glassy silicate network. We find that
the bond valence method is not well suitable to locate the sites, but allows
one to estimate the number of sites. Spatial regions of the glass determined as
accessible for the Li ions by the bond valence method can capture up to 90% of
the diffusion path. These regions however entail a significant fraction that
does not belong to the diffusion path. Because of this low specificity, care
must be taken to determine the diffusive motion of particles in amorphous
systems based on the bond valence method. The best identification of the
diffusion path is achieved by using a modified valence mismatch in the BV
analysis that takes into account that a Li ion favors equal partial valences to
the neighboring oxygen ions. Using this modified valence mismatch it is
possible to replace hard geometric constraints formerly applied in the BV
method. Further investigations are necessary to better understand the relation
between the complex structure of the host network and the ionic diffusion
paths.
