The effect of molecular dynamics sampling on the calculated observable gas-phase structures

Area of Science:

• Computational Chemistry
• Molecular Dynamics
• Quantum Mechanics

Background:

• Accurate prediction of molecular structures requires accounting for nuclear quantum effects in vibrational dynamics.
• Classical molecular dynamics methods often fail to capture these quantum effects, leading to inaccurate structural predictions.

Purpose of the Study:

• To compare the performance of various ab initio molecular dynamics (MD) sampling methods for calculating observable vibrationally-averaged gas-phase structures.
• To identify computationally feasible and accurate methods for predicting molecular structures, including benzene, naphthalene, and anthracene.

Main Methods:

• Tested Nose-Hoover (NH), canonical and quantum generalized-Langevin-equation (GLE) thermostats.
• Evaluated a posteriori quantum correction to classical trajectories.
• Compared results with path-integral molecular dynamics (PIMD) and experimental gas electron diffraction data.

Main Results:

• Classical MD methods neglecting quantum effects underestimate vibrational amplitudes, resulting in nonphysically narrow peaks in radial distribution functions.
• Quantum-corrected methods, specifically the quantum GLE thermostat and a posteriori corrections, accurately capture vibrational quantum effects.
• These quantum-corrected methods closely reproduce PIMD and experimental results, demonstrating their accuracy and feasibility.

Conclusions:

• Quantum-corrected MD methods are recommended for calculating observable gas-phase molecular structures due to their accuracy and computational feasibility.
• The quantum GLE thermostat shows promise for gas-phase calculations, as its parameters were originally fitted for condensed-phase systems.
• Combining high-level electronic structure theory with MD-derived vibrational corrections yields highly accurate molecular structures.