Total energy of trigonal and tetragonal cobalt

The electronic structures of bulk trigonal, tetragonal, and hcp cobalt are calculated from first principles using density-functional theory. The resul ts are used to predict lattice spacings, magnetic moments, and elastic prop erties. Attention is focused on the bcc and fee structures, which are speci al cases of both the trigonal and tetragonal structures. An energy minimum is found around the fee structure with properties in agreement with previou s calculations and experiments. The bcc structure does not correspond to an energy minimum, and is therefore not a stable structure, with respect to t etragonal distortions. Our extensive calculations confirm the results of pr evious, more limited, density-functional calculations and are in contrast w ith experimental results that found metastable bce cobalt thin films. [S016 3-1829(99)01931-1].