Molecular Dynamics Driven by the Many-Body Expansion (MBE-MD)

Area of Science:

• Computational Chemistry
• Molecular Dynamics
• Quantum Dynamics

Background:

• Accurate simulation of molecular dynamics requires precise energy and force calculations.
• The many-body expansion (MBE) offers a potential route to reduce computational cost in simulations.

Purpose of the Study:

• To develop and apply a protocol for classical and nuclear quantum dynamics using MBE for energy and force generation.
• To evaluate the accuracy of the MBE approach for water clusters compared to full simulations.

Main Methods:

• Implementation of a many-body expansion (MBE) molecular dynamics (MD) protocol.
• Application to water clusters using TTM2.1-F and MB-Pol interaction potentials at various temperatures.
• Comparison of MBE-approximated energies and vibrational density of states with full simulations.

Main Results:

• Thermally averaged potential energy converges with the full simulation up to the four-body MBE term.
• Three-body terms contribute significantly (~20%) to energy; four-body terms are essential for quantitative accuracy (~2%).
• Harmonic frequencies are accurate to within cm^-1 at the four-body level; anharmonic frequencies require four-body description for OH-stretching.

Conclusions:

• The MBE-MD protocol, particularly with four-body terms, provides accurate energetics and vibrational spectra for water clusters.
• The method shows promise for highly accurate ab initio MD simulations across a broader range of molecular systems.
• Computational savings are realized when underlying electronic structure methods scale at least as N⁴.