KOPPEL

A further model Hamiltonian that is tailored for the treatment of non-adiabatic systems is the vibronic coupling (VC) model of Koppel et al. [65]. This provides an analytic expression for PES coupled by non-adiabatic effects, which can be fitted to ab initio calculations using only a few data points. As a result, it is a useful tool in the description of photochemical systems. It is also very useful in the development of dynamics methods, as it provides realistic global surfaces that can be used both for exact quantum wavepacket dynamics and more approximate methods. 

R. A. Greenkorn, L. B. Koppel, and S. Raghavan, "Heat Exchanger Network Synthesis—A Thermodynamic Approach," 71 stAlChE Meeting, Miami, Fla., 1978. 

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