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We study the influence of the softness of the interparticle interactions onthe fragility of a glass former, by considering three model binary mixtureglass formers. The interaction potential between particles is a modifiedLennard-Jones type potential, with the repulsive part of the potential varyingwith an inverse power $q$ of the interparticle distance, and the attractivepart varying with an inverse power $p$. We consider the combinations (12,11)(model I), (12,6) (model II) and (8,5) (model III) for (q,p) such that theinteraction potential becomes softer from model I to III. We evaluate thekinetic fragilities from the temperature variation of diffusion coefficientsand relaxation times, and a thermodynamic fragility from the temperaturevariation of the configuration entropy. We find that the kinetic fragilityincreases with increasing softness of the potential, consistent with previousresults for these model systems, but at variance with the thermodynamicfragility, which decreases with increasing softness of the interactions, aswell as expectations from earlier results. We rationalize our results byconsidering the full form of the Adam-Gibbs relation, which requires, inaddition to the temperature dependence of the configuration entropy, knowledgeof the high temperature activation energies ino rder to determine fragility. Weshow that consideration of the scaling of the high temperature activationenergy with the liquid density, analyzed in recent studies, provides a partialrationalization of the observed behavior.

Dependence of the fragility of a glass former on the softness of interparticle interactions