The preferable configuration and electronic structure of several types of free radical functionalized boron nitride nanotubes (BNNTs) were investigated by using density functional theory computations. All the free radicals have strong interaction with B atom in the tube, in spite of the electroaffinity of the radicals. However, though a large charge is transferred from tubes to NH2, OH or CN radicals, little change happens to the electronic structure of BNNTs, while COOH and COCl radicals introduce halffilled impurity levels around the Fermi level. Higher functionalization concentration leads to multiple impurity states around the Fermi level, and makes BNNTs p-type semiconductors.
