The pyrazine molecule contains a classic example of vibronic coupling. Two states, which are close in energy, are coupled by motion along one vibrational mode, resulting in a broad spectrum for the upper state. This system can be described using the simple vibronic-coupling model Hamiltonian.

In this tutorial, we use a simple 4-mode 2-state model. This qualitatively reproduces the experimental spectrum after the addition of phenomenological broadening. The calculation takes the ground state wavefunction (here a simple product of gaussians as the ground state surface is harmonic), and places it on the S2 excited surface. Propagation then takes place, and rapid population transfer to the S1 state is observed. Finally, the spectrum of the model system is calculated.

## Software Used

### MCTDH

MCTDH stands for Multi Configuration Time Dependent Hartree. MCTDH is a general algorithm to solve the time-dependent Schrödinger equation for multidimensional dynamical systems consisting of distinguishable particles. MCTDH can thus determine the quantal motion of the nuclei of a molecular system evolving on one or several coupled electronic potential energy surfaces. MCTDH by its very nature is an approximate method. However, it can be made as accurate as any competing method, but its numerical efficiency deteriorates with growing accuracy.

For more details see MCTDH .

## Model New Results

## References

## Related Models

Following are some related models available for cloning/copying by anyone: