Fernández Pérez, Luis AntonioGordillo Guerrero, A.Martín Mayor, VíctorRuiz Lorenzo, J. J.2023-06-202023-06-2020080094-243x10.1063/1.3033359https://hdl.handle.net/20.500.14352/51917© 2008 American Institute of Physics. BIFI International Congress (111th. 2008. Zaragoza, Spain). This work has been partially supported by MEC through contracts No. FIS2004-0I399, FIS2006-08533-C03, FIS2007-60977 and by CAM and BSCH. Computer time was obtained at BIFI, UCM and UEx and (~ 50%) in the Mare Nostrum. The authors thankfully acknowledge the computer resources and technical expertise provided by the Barcelona Supercomputing Center.We present a detailed numerical study on the effects of adding quenched impurities to a three dimensional system which in the pure case undergoes a strong first order phase transition (specifically, the ferromagnetic/paramagnetic transition of the site-diluted four states Potts model). We can state that the transition remains first-order in the presence of quenched disorder (a small amount of it) but it turns out to be second order as more impurities are added. A tricritical point, which is studied by means of Finite-Size Scaling, separates the first-order and second-order parts of the critical line. The results were made possible by a new definition of the disorder average that avoids the diverging-variance probability distributions that arise using the standard methodology. We also made use of a recently proposed microcanonical Monte Carlo method in which entropy, instead of free energy, is the basic quantity.engjournal articlehttp://dx.doi.org/10.1063/1.3033359http://scitation.aip.org/open access5351-73Field ising-modelBond Potts modelsCritical exponentsCritical-behaviorMonte-Carlo.Física (Física)Física-Modelos matemáticos22 Física