Try with GaussSum by taking output file. I m not sure whether it works for NwChem or not but It works for Gaussian.

thanks your answer, gaussum works... alternative for gaussum is chemissian http://chemissian.com/

Assuming you have calculated the coefficient C for a particular transition, then, for a closed shell system the percentage contribution of that configuration to the resulting excited state is obtained as 2*C^2*100. Be careful, this does not hold for open shell systems.