Getting the parameters from lmfit
Including a complete, minimal example that shows what you are doing is always a good idea.  In addition, your subject is not a good reflection of your question. You have now asked enough questions about lmfit here on SO to know better. 
You probably want to use ModelResult.eval() to evaluate the ModelResult (probably your out) for a given independent variable.  If you need more help, ask an answerable question that might be useful to others...
I am doing a fit in python with lmfit and after I define my model (i.e. the functio I want to use for the fit) I do out = model.fit(...) and in order to visualize the result I do plt.plot(x, out.best_fit). This works fine, however this computes the value of the function only at the points used for the fit. How can I apply the parameters of the fit to any x vector (to get a smoother curve), something like x_1 = np.arange(xi,xf,i), plt.plot(x_1,out.best_fit(x_1))? Thank you!