respectively, where b ( †) is the lowering (raising) operator. Here dissipation is defined as the relaxation of the system excitation energy through coupling to environmental degrees of freedom. Dephasing occurs as a direct consequence of environmentally induced stochastic perturbations driving the system's potential energy surface away from equilibrium. This manifests physically as a decoherence of wavepackets. A reorganisation energy, ℏλ = 1 2 ℏω 0 ∆ 2 0 , is induced through the displacement of the excited state potential, with respect to the ground state minimum, along the nuclear coordinate by ∆ 0 . This generates the site (diabatic) basis monomer Hamiltonian in which there is a localisation of states onto a particular potential energy surface. This Hamiltonian is transformed into the vibronic (adiabatic) basis.