As a concrete example of the above-mentioned MQC dynamics applied to a "realistic ab initio" system, the authors of Ref. 154 explore the one-electron Shin-Metiu model system (shown in Fig. ). This model system is composed of four species: two heavy particles fixed-in-space (red and blue) with unit positive charge as well as a mobile and classical proton (black) and a quantum mechanical electron (green). Below the system, Fig. shows the potential energy of the proton (black curve) as well as that of the electron (green curve) as a function of the proton coordinate R . For a detailed explanation of the parameters of this asymmetric Shin-Metiu model, we refer the interested reader to Ref. 154. The two lowest energy Born-Oppenheimer potential energy surfaces (i.e., the ground and first excited adiabatic states), E g and E e , are shown in Fig. , which exhibit an avoided crossing near R = 2.0 a.u.