For the long-ranged combined Coulomb and Lennard-Jones potentials: time used vs. position errors versus time used for the total number of particles N = 4096 (left) and the time used in solving the force-balance equations vs. the total number of particles (right). Here, error is relative to the molecular dynamics simulation, QC refers to the quasicontinuum method, and QC-QR to the "quadrature"-rule approximation to the QC method. In the figure to the right the solid (dashed) lines are for 65 (resp. 17) representative particles. Note that for the same error, the QC-QR method requires much less time relative to the QC method, the time used for the QC-QR method depends on the number of representative particles but is largely independent of the total number of particles, and the QC method is highly dependent on the number of total number of particles. Information about the cluster summations approximation to the QC method is not given because that method behave very much like the QC method for the long-range interaction case.