  We employed ab-initio molecular dynamics to directly simulate the effects of
Ag alloying ($\sim5%$ Ag concentration) on the phase change properties of
Ge$_{2}$Sb$_{2}$Te$_{5}$. The short range order is preserved, whereas a slight
improvement in the chemical order is observed. A slight decrease in the
fraction of tetrahedral Ge (sp$^{3}$ bonding) is reflected in the reduction of
the optical band gap and in the increased dielectric constant. Simulations of
the amorphous to crystalline phase change cycle revealed the fact that the
crystallization speed in Ag$_{0.5}$Ge$_{2}$Sb$_{2}$Te$_{5}$ is no less than
that in Ge$_{2}$Sb$_{2}$Te$_{5}$. Moreover, the smaller density difference and
the larger energy difference between the two phases of
Ag$_{0.5}$Ge$_{2}$Sb$_{2}$Te$_{5}$ (compared to Ge$_{2}$Sb$_{2}$Te$_{5}$)
suggest a smaller residual stress in devices due to phase transition and
improved thermal stability for Ag$_{0.5}$Ge$_{2}$Sb$_{2}$Te$_{5}$. The
potential viability of this material suggests the need for a wide exploration
of alternative phase change memory materials.
