When performing a combined QM/MM simulation, the molecular system is divided into QM and MM regions as shown in Figure 1-1a. We will refer to the total hybrid system as the 'full system' or sometimes we will refer to it as the 'real system'. The 'QM model system' is the capped system for which the electronic structure calculation is performed. Figure 1-1a shows the full system and Figure 1-1b depicts the corresponding QM model system.
