Implementation of the projector augmented-wave method in the ABINIT code: Application to the study of iron under pressure

The projector augmented wave method (PAW), introduced for the first time by Blöchl [P. Blöchl, Phys. Rev. B 50 (1994) 17953], has been implemented in the ABINIT code [X. Gonze, J.-M. Beuken, R. Caracas, F. Detraux, M. Fuchs, G.-M. Rignanese, L. Sindic, M. Verstaete, G. Zerah, F. Jollet, et al., Comput. Mater. Sci. 25 (2002) 478]. This implementation allows self-consistent calculations of the electronic structure of a periodic solid within the density functional theory (DFT), including the analytic calculation of forces and stresses. Geometry optimization and molecular dynamics are also available. We present here the details of the implementation, including the analytic formula for forces and stresses. Results concerning the study of iron under pressure are presented to validate the implementation.