Abstract
We study iron clusters containing 2 ∼ 13 atoms by ab initio calculations with both collinear and noncollinear magnetic methods. Spin-orbit coupling is only available in the noncollinear method. After full structural relaxations, it is found that atom positions derived from the noncollinear method have better stability in all clusters, including those having coparallel spin arrangements. Binding energies of clusters calculated by the noncollinear method are also 17.3 ∼ 19.8 meV/atom lower, which are too large to ignore. By comparing the magnetic properties and electronic structures from the two methods, we believe that the difference has resulted from spin-orbit coupling. We recommend reconsidering the importance of the noncollinear magnetic method with spin-orbit coupling in magnetic systems. Especially in transition metal clusters when atom positions and energy values are important for determining the crucial properties.