15 July 2002 Physics Letters A 299 (2002) 660–665 www.elsevier.com/locate/pla Relationship between glass transition and rigidity in a binary associative fluid A. Huerta, G.G. Naumis ∗ Instituto de Física, Universidad Nacional Autónoma de México (UNAM), Apartado Postal 20-364, 01000 Distrito Federal, México, Mexico Received 18 January 2002; accepted 18 April 2002 Communicated by J. Flouquet Abstract Using Monte Carlo simulations in a binary associative fluid, we study the effects of connectivity on the glass transition. The results show that this transition occurs near the rigidity transition, when the number of geometrical constraints due to bonding and excluded volume in a given temperature of the simulation, is equal to the degrees of freedom available in the configurational space. These results are interpreted within the energy landscape paradigm. We also show that the average coordination number is a good parameter to describe many thermodynamical properties of the glass formation.  2002 Published by Elsevier Science B.V. PACS: 64.70.Pf; 64.60.-i; 05.70.-a Glass transition (GT) is a process where an amor- phous solid is formed by supercooling a melt, and re- mains as one of the most fascinating problems in solid state [1]. Not all materials are able to form glasses, and many semi-empirical criteria have been proposed in order to explain the ability of a material to reach the glassy state [2], because there are many factors in- volved in the process. Of these, one important is the speed of cooling. A slow speed means that the system has time to explore different states of the phase space and a glass cannot be formed, since the crystal has a lower free energy. To form a glass, the melt must be cooled fast enough. The GT is not considered as a true * Corresponding author. E-mail address: naumis@fenix.ifisicacu.unam.mx (G.G. Naumis). phase transition, although there are jumps in the spe- cific heat or in the thermal expansion coefficient [3]. A lot of attention has been given to the problem of finding the physical and chemical factors that de- termine the temperature where it occurs, called GT temperature (T g ). Among these factors, the chemi- cal composition is fundamental. Chalcogenide glasses (formed with elements of the VI column) are a bench- mark test for understanding the effects of the chem- ical composition [4]. For example, T g can be raised or lowered by adding impurities, and the fragility of the glass can be changed from strong to fragile [5]. For these changes, a method based on the statistics of agglomeration [6,7] succeeded in obtaining the empir- ical modified Gibbs–DiMarzio law that accounts for the relation between T g and the concentration of mod- ifiers [8]. The method predicts the characteristic con- stant that appears in the law for almost any chalco- 0375-9601/02/$ – see front matter  2002 Published by Elsevier Science B.V. PII:S0375-9601(02)00519-4