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A reduced orbital method for large-system electronic structure calculations

A new method using a small fixed number (much less than the total number of electrons in the system) of orbitals to calculate the electronic structure of an arbitrarily large system is presented. For crystals, this method reduces to a conventional Brillouin zone k-point integration method with the total number of states of all the k-points equal to the number of orbitals used in this method. If one uses a fixed number of orbitals the total computational time is linear in the size of the system. The method is applied to two test systems using a plane wave basis and the results are compared with conventional methods.