A parallel implementation of the projector augmented plane wave (PAW) method with the applications to several transition metal complexes is presented. A unique aspect of our PAW code is that it can treat both charged and neutral cluster systems. We discuss how this is achieved via accurate numerical treatment of the Coulomb Green's function with free space boundary conditions. The strategy for parallelizing the PAW code is based on distributing the plane wave basis across processors. This is a versatile approach and is implemented using a parallel three-dimensional Fast Fourier Transformation (FFT). We report parallel performance analysis of our program and of the three-dimensional FFT's and discuss large-scale parallelization issues of the PAW code. Using a series of transition metal monoxides and dioxides, as well as two iron aqueous complexes, it is shown that a free space PAW code can give structural parameters and energies in good accord with Gaussian based methods. © 2002 Elsevier Science B.V. All rights reserved.