where α is a parameter that controls the magnitude of the displacement. The value of α is chosen to satisfy our trust region condition, which we describe below. Note that as with the standard SQP minimization method described above, we have replaced the gradient g with the extrapolated gradient gex and the approximate Hessian of the potential energy B with the approximate Hessian of the Lagrangian BL . This will result in a displacement vector s Q which is suitable for use in the null-space SQP minimization formalism. The right-hand side of equation 27 can be minimized by solving an eigenvalue problem, 36