STATIC AND DYNAMIC POLARIZABILITY CALCULATIONS FOR THE POLYYNE SERIES(C2NH2) WITH EXTRAPOLATION TO THE INFINITE CHAIN

We have calculated static and dynamic longitudinal polarizabilities, a lpha(zz)(-omega;omega), for the polyyne series, C2nH2, using both the uncorrelated random phase approximation and the correlated second-orde r polarization propagator approximation. The calculated polarizabiliti es are extrapolated to the value for the infinitely long chain using s even different extrapolation techniques. We employ both conventional s chemes, such as the fitting of simple polynomials, as well as new sche mes, such as the fitting of a Pade approximant, or purely mathematical ly motivated nonlinear sequence transformations which have not previou sly been used in connection with this property. For the direct fits, w here the number of parameters is the same as the number of points, we find that the most stable and reliable extrapolation schemes are to be found among the latter. (C) 1998 American Institute of Physics.