The atomic and electronic properties of the adsorption of furan (C4H4O) molecule on the Si(100)-(2 x 2) surface have been studied using ab initio calculations based on pseudopotential and density functional theory. We have considered two possible chemisorption mechanisms: (i) [4 + 2] and (ii) [2 + 2] cycloaddition reactions. We have found that the [4 + 2] interaction mechanism was energetically more favorable than the [2 + 2] mechanism, by about 0.2 eV/molecule. The average angle between the C=C double bond and Si(100) surface normal was found to be 22 degrees, which is somewhat smaller than the experimental value of 28 degrees, but somewhat bigger than other theoretical value of 19 degrees. The electronic band structure, chemical bonds, and theoretical scanning tunneling microscopy images have also been calculated. We have determined a total of six surface states (one unoccupied and five occupied) in the fundamental band gap. Our results are seen to be in good agreement with the recent near edge X-ray absorption fine structure and high resolution photoemission spectroscopy data. (C) 2008 Elsevier B.V. All rights reserved.