Here we want to document that FAMUSAMM actually provides an enhanced computational efficiency both as compared to SAMM as well as to the reference method which is characterized by exact evaluation of the Coulomb sum. To that aim we have carried out a series of test simulations for systems of varying size ranging from 500 to 40,000 atoms. We used the sequential version of EGO_VIII. All simulations were executed on a DEC-ALPHA 3300L (175 MHz) workstation equipped with 96 MB RAM. Figure 3 shows that the average computation time required for one MD integration step scales linearly with system size for systems comprising more than about 1,000 atoms.
For large systems comprising 36,000 atoms FAMUSAMM performs
four times faster than SAMM and as fast as a cut-off scheme
with a Å cut-off distance
while completely avoiding truncation artifacts. Here, the speed-up
with respect to SAMM is essentially achieved by the
multiple-time-step extrapolation of local Taylor expansions in the outer
distance classes. For this system FAMUSAMM executes by a factor of 60
faster than explicit evaluation of the Coulomb sum.
The subsequent Section describes, as a sample application
of FAMUSAMM, the study of a ligand-receptor unbinding process.