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PhD thesis in English

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2. Diagonalization of Transition Amplitudesy-15-10-5050.040.020-0.02-0.04y-15-10-5050.040.020-0.02-0.04101015-15 -10 -5 0 5 10 15x15-15 -10 -5 0 5 10 15xy-15-10-5050.040.020-0.02-0.04y-15-10-5050.040.020-0.02-0.04101015-15 -10 -5 0 5 10 15x15-15 -10 -5 0 5 10 15xFigure 2.15: Density plots of level k = 1, 2, 3, 4 eigenstates of a d = 2 anharmonicpotential (2.36) obta<strong>in</strong>ed us<strong>in</strong>g p = 21 effective action. The parameters are k 2 =−0.1025, k 4 = k exp4 , L = 20, ∆ = 0.25, t = 0.2.potential (2.36). Due to the high degeneracy of energy eigenstates <strong>in</strong> d = 2, thehistogram of numerically found energy levels conta<strong>in</strong>s enough statistics over thewhole region of energies, and therefore can be used for assessment of the quality ofnumerical spectra. As we see, the agreement is better and better when we use f<strong>in</strong>erspace discretization. Depend<strong>in</strong>g on the needed number of energy levels and maximalvalue of the energy considered to be relevant for the calculation we can chooseappropriate values of discretization parameters that will provide reliable numericalresults up to desired energy value. For example, for the choice of discretizationparameters L = 14, ∆ = 0.14, we can reliably use energy levels up to E ≈ 120.Fig. 2.16(bottom) shows the comparison of cumulative density of states n(E)calculated for numerically obta<strong>in</strong>ed results and <strong>in</strong> semiclassical approximation, by51

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