where Ĥ is the Hamiltonian operator, ψ is the system's wave function, and E is the total energy of a chemical species. Depending on the size of the system, E is not trivial to calculate and some approximations to the Schrödinger equation are made to be able to solve it numerically, to be discussed in Section 3.1 Once a species' energy is known, intrinsic solvent effect can then be determined. The differential solvation between reactants and transition states causes a energetic change between these two species, modifying ∆G ‡ when changing phases and thus affecting the reaction rate as indicated in equation ( ) and illustrated in Fig. . Several computational methods are commonly utilized for obtaining geometries of reactants and transition states, and their properties, i.e. electronic energies and frequencies.