Low-Lying Electronic Excitations and Nonlinear Optic Properties of   Polymers via Symmetrized Density Matrix Renormalization Group Method
  A symmetrized Density Matrix Renormalization Group procedure together with the correction vector approach is shown to be highly accurate for obtaining dynamic linear and third order polarizabilities of one-dimensional Hubbard and $U-V$ models. The $U-V$ model is seen to show characteristically different third harmonic generation response in the CDW and SDW phases. This can be rationalized from the excitation spectrum of the systems. 
S. Ramasesha, Swapan K. Pati, H. R. Krishnamurthy (Indian Institute of   Science) Z. Shuai and J. L. Bredas (University of M...