33 lines
884 B
Python
33 lines
884 B
Python
#Program fitting the exchange interaction
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#Model curve: Bethe-Slater function
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import numpy as np, pylab, tkinter
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import matplotlib.pyplot as plt
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from scipy.optimize import curve_fit
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from decimal import *
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print("Loop begin")
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#Definition of the Bethe-Slater function
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def func(x,a,b,c):
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return 4*a*((x/c)**2)*(1-b*(x/c)**2)*np.exp(-(x/c)**2)
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#Exchange coeff table (data to fit)
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rdata, Jdata = np.loadtxt('exchange_bcc_iron.dat', usecols=(0,1), unpack=True)
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plt.plot(rdata, Jdata, 'b-', label='data')
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#Perform the fit
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popt, pcov = curve_fit(func, rdata, Jdata, bounds=(0, [500.,5.,5.]))
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plt.plot(rdata, func(rdata, *popt), 'r--', label='fit')
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#Print the fitted params
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print("Parameters: a={:.10} (in meV), b={:.10} (adim), c={:.10} (in Ang)".format(*popt))
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#Ploting the result
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plt.xlabel('r_ij')
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pylab.xlim([0,6.5])
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plt.ylabel('J_ij')
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plt.legend()
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plt.show()
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print("Loop end")
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