Models discussed in this section are generally smaller than the τ 2B models described in Section 3 .2, which impacts both the computational load and the time required for processing. This is clearly reflected in the timing data in Table , where MBE(2) calculations using the 6 Å model require on 10 h for the largest protein-ligand complex, as compared to 22 h for our preferred τ 2B -derived model.