We describe our studies of two methods for generating bias potentials for use in hyperdynamis simulations. In the first method, first reported by Steiner, eet al, the bias potential is the additional energy needed to keep the total potential energy above a fixed level. Tis potential exerts a negligible computational load and is very easy to code. The second technique involves computing the iterative hessian-based bias otential as usual, but including in those calculations only the atoms in a small "active region" that surrounds the area in which a state transition is expected to occur. This "subspace hyperdynamics" method is less costly than full HD. The extra computational effort required for HD scales as the size of the active region(s), instead of with the size of the entire simulation domain.
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