FAST ITERATIVE DIAGONALIZATION OF NONLOCAL PSEUDOPOTENTIAL HAMILTONIANS USING THE FAST FOURIER TRANSFORMATION

Many electronic-structure calculations are using nonlocal pseudopotentials in connection with iterative diagonalization methods. The most time-consuming steps in those calculations are the calculations of the n2 matrix elements and the subsequent diagonalization of this matrix, which requires the repeated calculation of matrix vector products. Using conventional matrix multiplication this takes an order of n2 operations. We present a new technique which significantly reduces the computational effort for k points of high symmetry. Since the Hamiltonian is defined as an operator, no individual matrix elements are required. Furthermore, it allows the use of the fast Fourier transform to do the matrix times vector multiplication. © 1990 The American Physical Society.