Finite-Temperature Correlation Functions Obtained from Combined Real- and Imaginary-Time Propagation of Variational...

Area of Science:

• Quantum mechanics
• Computational chemistry
• Statistical mechanics

Background:

• Calculating thermal correlation functions is crucial for understanding molecular dynamics.
• Strongly anharmonic systems and quantum tunneling pose significant challenges for traditional computational methods.

Purpose of the Study:

• To evaluate the variational Gaussian wavepacket approximation (VGA) for real- and imaginary-time dynamics.
• To assess VGA's capability in calculating thermal correlation functions for anharmonic systems.
• To compare VGA with existing methods like ring polymer molecular dynamics and the classical Wigner method.

Main Methods:

• Application of the variational Gaussian wavepacket approximation (VGA) for both real- and imaginary-time propagation.
• Investigation of anharmonic potentials (quartic and double-well) at various temperatures.
• Calculation of thermal correlation functions.

Main Results:

• The VGA method demonstrates partial ability to account for quantum tunneling in anharmonic systems.
• VGA successfully calculates thermal correlation functions where other methods, such as ring polymer molecular dynamics and the classical Wigner method, fail.
• This study highlights the novel application of VGA for both Boltzmann operator and real-time propagation.

Conclusions:

• The variational Gaussian wavepacket approximation (VGA) offers a promising approach for simulating quantum dynamics in complex molecular systems.
• VGA's ability to handle tunneling makes it superior to other methods for specific anharmonic systems.
• The method is well-suited for molecular systems with many atoms, advancing computational chemistry and statistical mechanics.