We present an efficient postprocessing method for calculating the electronic structure of nanosystems based on the divide-and-conquer approach to density functional theory (DC-DFT), in which a system is divided into subsystems whose electronic structure is solved separately. In this postprocess, the Kohn-Sham Hamiltonian of the total system is easily derived from the orbitals and orbital energies of subsystems obtained by DC-DFT without time-consuming and redundant computation. The resultant orbitals spatially extended over the total system are described as linear combinations of the orbitals of the subsystems. The size of the Hamiltonian matrix can be much reduced from that for the conventional calculation, so our method is fast and applicable to general huge systems for investigating the nature of electronic states.

• Received 9 November 2016

DOI:https://doi.org/10.1103/PhysRevB.95.045106