Starting from the long-tail in molecular liquid velocity correlation function

the same long-tail in the stress correlation function of molecular liquid is obtained by computer simulation.By using the scaling picture

it is shown that the long-range correlations in a polymer chain and the long-tail in velocity/stress correlation function in the molecular liquid share the same physical mechanism.Both of the velocity/stress correlation function and the bond vector correlation function have analogous characteristics.Instead of the exponential decay predicted by the classic model of the random walk

the new power-law decay of bond-vector correlation function in polymer chains is clearly explained.The bond vector correlation functions for chains in good and theta solvents are decayed as a power law with exponent 2v -2 and -3/2

respectively.