The modified embedded-atom method, a first nearest-neighbor semiempirical model for atomic potentials, can describe the physical properties of a wide range of elements and alloys with various lattice structures. However, the model is not quite successful for bcc metals in that it predicts the order among the size of low index surface energies incorrectly and that it generates a structure more stable than bcc for some bcc metals. In order to remove the problems, the formalism has been extended so that the second nearest neighbor interactions are taken into consideration. New parameters for Fe and comparisons between calculated and experimental physical properties of Fe are presented.