The divide‐and‐conquer density‐functional method recently developed by Yang is applied to the calculations of internal rotation energies and density of electronic states of a tetrapeptide. The method, on comparison with the conventional Kohn–Sham method, is found to be capable of accurately describing the density of states and the small electronic energy changes in the internal rotation. The calculations further demonstrate the promise of the method for calculations of large systems beyond the reach of conventional methods. © 1992, American Institute of Physics. All rights reserved.