محاسبات مونت كارلوي كوانتومي براي نانو ذرات مغناطيسي

چكيده انگليسي :

Maryam Balou i m balou i@ph iut ac ir Department of Physics Isfahan University of Te nology Isfahan 84156 83111 IranDegree M Sc Supervisor Dr M Alaei Abstract During the last 15 years transition metal diatomic molecules have been systems of great interestto both theoreticians and experimentalists e main motivation of this study is to nd out what isthe smallest particle size for data storages It is understood that low cost computing method to studyclusters and larger systems is density functional theory Although many studies have been performedfor variety of elements by the usage of density functional theory the accuracy of these calculationsis not discussed as well e starting point of this study is diatomic molecules e studies showthat Density functional theory the ground state electronic instead of the 4s2 3dn predicted to form a4s1 3dn 1 and it is the greatest defect of density functional theory in the case of this group of elements e results for cobalt s dimer is associated with greater uncertainty erefore we study Co2 and thenearest neighbors Fe2 and Ni2 Calculations has been performed by using computational pa agessu as Gaussian and aug cc pvdz wave function on the best multiplicity In order to studythe correlation e ects by considering a xed share ex ange and various correlations we calculate theground state properties then we study the energy gap distribute arge and N BO calculations evarious functional ex ange correlaton anticipate di rent results Since the orbitals lling is di erent we get di erent results that show Correlation e ects in transition metals has a large e ect on the energyof the ground state properties thus using a more accurate method is needed to perform su studies Up to data di usion Monte Carlo method is the most accurate tools available In these calculations we use the wave function to obtion the ground state energy e wave function is composed of twoparts Determinant and Jastrow factor Parameters are dependent on the energy of the wave function At ea step exerting variation of parameters will anged energy that is negative compared to theprevious state Calculations are performed with statistical methods ergo it has some aws We triedto minimize sources of error e main sources of error is Slater Determinant time step and jastrowfactor en we nd the appropriate wave function for di usion Monte Carlo calculations using thecomputational pa age CASIN O in two di erent time step and repeat it by extrapolation method the ground state energy at zero gain Finally the energy in several points the curve potential of using the Morse potential function will t Rydbrg Ground state properties of the gain the optimized bond lengths for the two cobaltatoms is 1 35A Results are repeated for the other spin states Unfortunately the results for the twoni el atoms does not comply with expectations and has a slight discripancies with expreimental data therefore the best methods of computational emistry calculations in terms of accuracy is antumMonte Carlo e results con rmed Monte Carlo results In the last step the Heisenberg ex ange interaction Hamiltonian Frmghnatys mode A modeNtyfrvmghnatys has been used e results of this interaction decreases exponentially by increasingdistance Keywords Density functional theory Di usion of Monte Carlo diatomic of transitional metal Hyzenberg model wave function Variational method

بلوچي، مريم

محاسبات مونت كارلوي كوانتومي براي نانو ذرات مغناطيسي

نظريه تابعي چگالي , دواتمي واسطه , مدل هايزنبرگ , تابع موج , وردش