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A diabatic representation describes coupled electronic states using a basis chosen to vary smoothly with nuclear geometry, often reducing the derivative couplings that appear in an adiabatic basis. In exchange, the electronic energy matrix generally has off-diagonal entries. It is a representation of coupled states, not a claim that the states never interact.

For a two-state example with nuclear coordinate $R$,The diagonal diabatic curves cross at $R=0$, while their coupled adiabatic eigenvalues have an avoided crossing when $V\ne 0$. This makes electron transfer and nonadiabatic reaction models easier to interpret. An exactly derivative-coupling-free basis need not exist globally for every multidimensional molecular problem.

Elham Nour Ghassemi investigated the two lowest electronic states of the lithium trimer using multireference calculations. A diabatic representation converts the behaviour near a conical intersection into a form suitable for studying coupled nuclear and electronic motion.^[ref]