[Pw_forum] questions about Raman tensor

[li yan]

dear all,
  i want to follow the example15 to study how to calculate the Raman intensities. i have three questions about that. thank you for your answers to any of the three questions.
 (1) i cannot understand the selection "b_length", could you please give me some papers about that.
 (2) whether the nonlinear susceptibility is defined as the first order derivative of the polarization with respect to the displacements of the atoms.
(3) in the file alas.ram, to every atom, there are three 3*3 matrix. whether these matrixes are defined as the Taylor expansion of the polarization with respect to the displacements of the atoms.
 

		
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