1998 Annual Report
Grand Challenge Projects Materials, Methods, Microstructure, and Magnetism G. Malcolm Stocks, Oak Ridge National Laboratory
Bruce N. Harmon, Ames Laboratory/Iowa State University
Michael Weinert, Brookhaven National Laboratory
Figure 1. 512-atom base-centered cubic iron system. The left frame shows the self-consistent field magnetic moments for the atoms, while the right frame shows the corresponding constraining fields. Atom positions are denoted by spheres, magnetic moments by arrows, and constraining fields by cones. (Click either image for larger version.) Research Objectives To develop first-principles quantum mechanical methods for addressing materials problems microscopically, especially the relationship between technical magnetic properties and microstructure. Towards this goal are major problems involving microstructure (independent of magnetism), magnetism (independent of microstructure), giant magneto-resistance, and thermal properties. Computational Approach Accomplishments A new constrained local moment (CLM) theory of non-equilibrium states in metallic magnets has been developed that places a recent proposal of our co-workers at Ames Laboratory for first-principles spin dynamics (SD) on firm theoretical foundations. In SD, non-equilibrium "local moments" (for example, in magnets above the Curie temperature, or in the presence of an external field) evolve from one time step to the next according to a classical equation of motion. As originally formulated, the instantaneous magnetization states that are being evolved were not properly defined within density functional theory. The CLM theory properly formulates SD within constrained density functional theory. Local constraining fields are introduced, the purpose of which is to force the local moments to point in directions required at a particular time step of SD. A general algorithm for finding the constraining fields has been developed. | |
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