Khelifi, Okacha2019-05-152019-05-152018-06-28salle des thesesms-530-41-01https://dspace.univ-tlemcen.dz/handle/112/14175CDThe densitymatrixrenormalizationgroupmethodhasbecomeinthepastthirtyyearsa stronger numericaltoolforthestudyofstaticanddynamicphysicalpropertiesoffundamental physicssystems.Theapplicationofthismethodtoanantiferromagneticspinchainwithin the Heisenbergmodelformagneticsystemsspinsallowsustoreproducesomewellknown theoretical resultsaboutrelativelylongspinchainscomaparedtothosediagonalzableusing standard routines.Also,thenumericalstudyallowsustocon rmtheexistenceofanenergy gap fora s = 1-spin chain(haldaneconjecture),butthenonexistenceofaanenergygapfora s = 1 21-spin chain.Thee ectofbothperiopdicandopenboundaryconditionsonthebehavior of theenergyspectraofthespinsystemisstudied.Also,thee ectofrandomcouplingonthe behaviorosenergylevelofaspinsystemisstudied.Intheotherhand,alinear tallowsusto write anexpressionofthegroundstateenergyasafunctionofthelengthofthespinchain.frApplication la méthode renormalisation par matrice densité chaine spins cadre modèle d'HeisenbergThesis