Good software to perform simulations on polymer (absorption spectra)?
It depends very significantly on what you want to accomplish.

I'm not going to suggest software, since there are many programs that can (and are) used to predict optical absorption spectra of conjugated polymers.

First, you can either approximate the properties of the polymer by running several calculations on oligomers (e.g., dimer, trimer, tetramer, etc.) and extrapolating the polymer band gap. Because conjugated polymers are similar to the particle-in-a-box model, you can roughly plot the HOMO-LUMO gap or excitation energy vs. 1/(# of repeat units) and get an approximately linear fit.

If you want more information, you could instead run a calculation on a polymer in a periodic unit cell, which will give you the electronic structure of the infinite system (but no information on disorder).

As suggested in the comment above, you can use multiple programs and different computational approaches depending on:


What kind of polymer
What kind of information you want
What computational resources you have
How accurately you want the information


The two most common methods for predicting optical absorption energies are the ZINDO/S semiempirical method, and TDDFT. The latter is more accurate particularly for predicting absorption intensity from the oscillator strength of the excitation energies.