Equilibrium-nonequilibrium ring-polymer molecular dynamics for nonlinear spectroscopy

Area of Science:

• Computational Chemistry
• Spectroscopy
• Quantum Dynamics

Background:

• Two-dimensional Raman and terahertz-Raman spectroscopy reveal molecular insights.
• Simulating condensed-phase systems is computationally expensive, hindering theoretical validation.
• Incorporating quantum mechanics in simulations is crucial but challenging.

Purpose of the Study:

• To present a practical computational method for simulating nonlinear optical spectroscopy.
• To account for nuclear quantum effects in molecular dynamics simulations.
• To provide a computationally feasible alternative to existing methods.

Main Methods:

• Equilibrium-nonequilibrium ring-polymer molecular dynamics (RPMD).
• Calculation of the two-time response function for nonlinear optical spectroscopy.
• Comparison with classical and double Kubo transformed (DKT) methods.

Main Results:

• The equilibrium-nonequilibrium RPMD method accurately includes nuclear quantum effects.
• The method is exact in the classical limit, reducing to established classical dynamics.
• Benchmark calculations show advantages over classical and DKT approaches.

Conclusions:

• Equilibrium-nonequilibrium RPMD offers a practical way to incorporate quantum effects in spectroscopy simulations.
• The method simplifies theoretical analysis by avoiding the need for specific Kubo transformed correlation functions.
• This work enables the application of real-time path-integral techniques to multidimensional spectroscopy.