Wigner Distribution by Adiabatic Switching in Normal Mode or Cartesian Coordinates and Molecular Applications

Area of Science:

• Computational Chemistry
• Quantum Mechanics
• Molecular Dynamics

Background:

• The Wigner function is a key tool for quantum mechanical phase space descriptions.
• Accurate calculation of the Wigner function for polyatomic molecules is computationally challenging.
• Classical trajectory methods offer a computationally tractable alternative.

Purpose of the Study:

• To implement and validate the adiabatically switched Wigner (ASW) method for polyatomic molecules.
• To assess the accuracy of ASW in both normal mode and Cartesian coordinates.
• To demonstrate the utility of ASW for quasiclassical simulations and spectral analysis.

Main Methods:

• Classical trajectory simulations under an adiabatically switched potential.
• Application to a six-degree-of-freedom formaldehyde model (normal modes) and butyne model (Cartesian coordinates).
• Utilized an ab initio quartic potential energy surface and the CHARMM force field.

Main Results:

• ASW demonstrated high accuracy and reliability for equilibrium properties across a wide temperature range.
• The ASW distribution is invariant under classical evolution, suitable for quasiclassical simulations.
• A novel ASW-based procedure for complex-valued quasiclassical time correlation functions and vibrational spectra was described.

Conclusions:

• The ASW method provides a highly accurate and computationally efficient approximation to the Wigner function for polyatomic molecules.
• ASW is a versatile tool for studying molecular properties and dynamics using quasiclassical methods.
• This approach facilitates the calculation of complex-valued correlation functions and vibrational spectra.