We propose an ab initio molecular dynamics method combined with the multicanonical algorithm for enhanced conformation sampling of biomolecules. This method was applied to a system of a blocked alanine peptide, Ace-(Ala)(2)-NMe, in vacuo, and was proved to be more efficient in conformation sampling than a conventional ab initio molecular dynamics method. We calculated free-energy landscapes from the conformation ensemble and discussed their differences from classical simulations. In addition, we analyzed the fluctuations of atomic charges and demonstrated that there are significant correlations between atomic charges and the conformation of the peptide. (c) 2006 Elsevier B.V. All rights reserved.