Ground state energy, increase

Note Configuration Interaction significantly increases computing time. For calculations of ground-state energies, MINDO/3, MNDO, AMI, and PM3 methods may already include in their parameters some effects of Configuration Interaction. 

In contrast with protic solvents, which decrease the rates of SN2 reactions by lowering the ground-state energy of the nucleophile, polar aprotic solvents increase the rates of Sn2 reactions by raising the ground-state energy of the nucleophile. Acetonitrile (CH3CN), dimethylformamide ((Chy NCHO,... 

The size of the substituent R also influences the rate, with the rate increasing somewhat for both isomers as R becomes larger. It is believed that steric interactions with R are relieved as the C—O bond stretches. The rate acceleration reflects the higher ground state energy resulting from these steric interactions. 

Figure 2, together with Table 2, explains the fact that neither the shortened Si=Si bond length, with respect to Si-Si, nor the increased vibrational frequency is in contradiction to the above statement 3 because minimum and curvature of the ground state energy curve are hardly influenced by the avoided crossing. 

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