Magnetoelasticity of Fe: Possible failure ofab initioelectron theory with the local-spin-density approximation and with the generalized-gradient approximation

The magnetoelastic coupling constant B₂ and the related magnetostriction coefficient λ₁₁₁ of bcc Fe are calculated by the ab initio density functional electron theory in local-spin-density approximation and in generalized-gradient approximation. Both B₂ and λ₁₁₁ exhibit a wrong sign as compared to the available experimental data, indicating a possible deficiency of the two approximations for the exchange-correlation functional.