A new density functional approach for calculations of large systems is presented.The system under consideration is divided into regions which are relatively independent quantum mechanical subsystems and can be calculated individually by means of density functional method, taking into account the effects of the potentials and the Pauli repulsion from the other subsystems.The single particle equation proper to each subsystem is solved,
(F^K+F^K_p)C^K=S^KC^Kε^K K=A,B,C, …
where F^K, C^K, S^K, ε^K are the Fock matrix, the coefficient matrix of orbitals, the overlap matrix of the basis set and the energy eigenvalue matrix, respectively, related to subsystem K .The matrix F_p^K plays the role to constrain the occupied orbitals belonging to different subsystems to be orthogonal to each other.The generated orbitals are regionally localized.Assembling the calculated results from all subsystems yields the electronic structure information of the whole system.The effect of several factors on the calculation accuracy was studied through the calculation of several relatively larger molecules.It is found that the presented method is feasible, the truncation errors of basis sets can be eliminated essentially and accurate results can be generated by controlling the size of the regional basis sets.The presented method is a linear scaling algorithm for sufficiently large systems.Comparing with the existent methods based on the similar strategy, the present method is easier to be used in the study of some regions for special requirements.

Key words: density functional calculation, large system, computational method based on division, linear scaling algorithm