An improved peripheral orbital method for calculating the electronic structure of complex systems with a localised basis

An improved peripheral orbital method is described for calculating the electronic structure of complex systems which can be expressed with respect to a basis of localised orbitals. The method is an improvement on a previous one and is shown to produce results that can be very sensitive to the way in which the eigenvalue problem is block-diagonalised. This problem is eliminated in the improved method by reducing the number of approximations to the single one needed for a peripheral treatment to be applied. At the same time all the advantageous features of the previous method are retained and, in particular, the improved method does not involve any increase in computation time. The accuracy of the method is demonstrated by applying it to silicon.