Demos.MolElectronic.Pyrazine

WavePacket demo example: Internal conversion of pyrazine molecule

The ultrafast internal conversion from the S₂ (B_2u) to the S₁ (B_3u) electronic state of the pyrazine molecule (C₄N₂H₄) is believed to proceed via a low-lying conical intersection of the respective potential energy hypersurfaces. Note that this intersection is not(!) due to a Jahn-Teller effect but is only partially symmetry induced! In the 1990s years, the vibronic dynamics of this system has become a quasi-benchmark system for various numerical techniques to treat intramolecular non-adiabatic quantum dynamics.

The models of are adapted from
* work by R. Schneider and W. Domcke
* work by R. Schneider, W. Domcke, and H. Köppel

Three-dimensional model

The vibronic dynamics leading to the ultrafast S₂-S₁ internal conversion of pyrazine is modelled in terms of a two-state three-mode vibronic coupling Hamiltonian consisting of two totally symmetric (A_g) tuning modes and the only non-totally symmetric (B_1g) coupling mode. This model exhibits a conical intersection along a straight line in the plane spanned by the former two coordinates. It is found that the initial population of the upper (S₂) state decays on a femtosecond timescale in a non-exponential way exhibiting a rich variety of phenomena in ultrashort spectroscopy.

Diabatic initial state

• Animated wavepacket
• Input data file
• Logfile output

Adiabatic initial state

• Animated wavepacket
• Input data file
• Logfile output

Note that the visualization shows phase space portraits of reduced density matrices for each of the three internal coordinates. They are obtained by tracing the full density matrix over the remaining two coordinates. The lower plots show the traces of the squares of these density matrices. They can be understood as the degree of coherence of the dynamics in each mode. This measure is unity for fully coherent dynamics and it decays to zero if the interaction with the "bath" of the other modes lead to decoherence.