Different PDF approximations useful for LO Monte Carlo generators
  The goal of this study is to find a prescription for defining parton distributions (PDFs) which are most appropriate for use in those codes where only LO matrix elements (MEs) are used, as in many Monte Carlo generators. We describe a modification of LO PDFs, based on using alpha_S at NLO, a specific prescription of the coupling in the QCD evolution, and violation of the momentum sum rule. We compare results with the truth - the prediction using NLO for both MEs and PDFs, and the standard LO prediction, finding that the modified PDFs generally produce the best results. 
A. Sherstnev and R.S. Thorne