Full-potential calculations using the generalized gradient approximation: Structural properties of transition metals

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Abstract
The equilibrium volumes and bulk moduli of nonmagnetic 3d, 4d, and 5d transition metals have been calculated using a full-potential linear-muffin-tin-orbitals (FP-LMTO) method and the generalized gradient approximation (PW91) of Perdew and Wang [in Electronic Structure of Solids 1991, edited by P. Ziesche and H. Eschrig (Akademie Verlag, Berlin, 1991), Vol. 11]. The gradient-corrected FP-LMTO results are found to be superior to the corresponding local-density approximation (LDA) results in all transition-metal series. Furthermore, the atomic-spheres approximation (ASA) is found to yield larger equilibrium volumes and smaller bulk moduli than the FP method. The inaccuracies introduced by the ASA are of the same magnitude as the gradient corrections, suggesting that a FP treatment is important for gradient-corrected calculations. Excellent agreement with experiment is found for the c/a ratios of the hcp metals using both the LDA and the PW91, while for the fcc-bcc structural energy differences of 4d metals disagreement with semiempirical estimates remains.