Sum Over States with damping - another question



Dear CCL Readers,
      I would like modify my original question. My problem is
 that I am obtaining negative values for the imaginary part
 of gamma(-w;w,w,-w). Can someone explain the meaning of a
 negative value of this imaginary part?
      Thank you very much in advance. I will summarize if I
 receive any answer.
      Sincerely yours,
                    Gustavo L.C. Moura
               gustavo!at!mercury.chem.pitt.edu
 > Dear CCL readers,
 >      I am interested in doing Sum Over States calculations of
 > absorption of two photons. I have read several papers including
 > the paper by Orr and Ward in Molecular Physics 20, 513 (1971).
 > When comparing equation 43c from Orr and Ward with the equation
 > in more recent papers that cite Orr and Ward, I found different
 > signs in front of the damping factors (they are all negative).
 > My question is: can anyone explain the discrepancy in these
 > signs?
 >      Thank you very much in advance.
 >      Sincerely yours,
 >                    Gustavo L.C. Moura
 >               gustavo!at!mercury.chem.pitt.edu