Figure 2.

Gas phase profiles. Shown are the gas phase attack profiles of a chloride anion reacting with methyl chloride for both a range of different high-level quantum mechanical techniques (top) and with a variety of semi-empirical Hamiltonians (bottom) as compared to the experimentally known barrier. From the high-level data, M06-2X reproduces the barrier most accurately. The newly parameterized semi-empirical Hamiltonian (SRP) closely mimics the higher level data (shown as the dashed line) and captures the experimental barrier.