Hi everybody, I have calculated the second derivative matrix (3N*3N) for a water molecule (TIP3P), the output file is attached with this post. In this file, I obtained 45 values which correspond of the values of the matrix (because the matrix is symetric so we need only the half of the values). The last part represents the coordinates of the three atoms but I can't identify the signification of the values in the first part. Does anybody can help me please ? Thanks a lot !