We have developed a computationally efficient procedure for modeling of amorphous structures (a-Si), starting with a molecular dynamics simulation of crystalline silicon (c-Si) with a force field, followed by melting and ab initio electronic structure calculations at low temperatures. The radial distribution functions and static structure factors for our a-Si structures and the density of vibrational states are in good agreement with experimental values. New results on photoabsorbance for melted and final a-Si structures are compared with the c-Si structure, and a-Si shows broader but weaker absorption compared to c-Si. Our procedure should be equally applicable to other atomic structures. (C) 2013 Elsevier B.V. All rights reserved.