NVU dynamics. III. Simulating molecules at constant potential energy.

Area of Science:

• Molecular Dynamics Simulation
• Computational Chemistry
• Statistical Mechanics

Background:

• Standard molecular dynamics often uses energy-conserving NVE (Newtonian) or temperature-controlled NVT ensembles.
• Previous work introduced geodesic molecular dynamics (NVU) for atomic systems, demonstrating time-reversibility, symplecticity, and equivalence to NVE dynamics.
• NVU dynamics offers an alternative simulation method with desirable numerical properties.

Purpose of the Study:

• Extend geodesic molecular dynamics (NVU) to simulate molecular systems with rigid bonds at constant potential energy.
• Develop and test a novel NVU algorithm incorporating rigid bond constraints.
• Validate the performance and accuracy of the rigid-bond NVU algorithm against established methods.

Main Methods:

• Derivation of a new algorithm for simulating geodesic motion of molecules with rigid bonds.
• Testing the rigid-bond NVU algorithm on three distinct molecular models: an asymmetric dumbbell, o-terphenyl (OTP), and rigid SPC/E water.
• Comparison of simulation results with those obtained from Nosé-Hoover NVT dynamics.

Main Results:

• The rigid-bond NVU algorithm successfully conserves potential energy, bond lengths, and step length during long simulation runs.
• Simulation results from the NVU dynamics were found to be identical to those from Nosé-Hoover NVT dynamics.
• The study confirms that NVU dynamics is equivalent to NVE dynamics in the thermodynamic limit for molecular systems.

Conclusions:

• The developed rigid-bond NVU algorithm is a stable and accurate method for molecular dynamics simulations at constant potential energy.
• NVU dynamics provides a viable alternative to NVT methods, offering similar results while maintaining constant potential energy.
• This work extends the applicability of geodesic molecular dynamics to complex molecular systems, reinforcing its theoretical underpinnings.