Inertial extended-Lagrangian scheme for solving charge equilibration models.

Area of Science:

• Computational Chemistry
• Materials Science
• Molecular Dynamics

Background:

• Accurate charge equilibration is crucial for reactive force field (ReaxFF) simulations.
• The charge conservation constraint in ReaxFF necessitates solving complex linear equations at each time step.
• Existing methods can be computationally intensive, limiting simulation efficiency.

Purpose of the Study:

• To introduce and validate the inertial extended Lagrangian/self-consistent field (iEL-SCF) scheme for charge equilibration in LAMMPS.
• To assess the efficiency improvements of iEL-SCF compared to traditional solvers.
• To demonstrate the applicability of iEL-SCF across diverse chemical systems.

Main Methods:

• Implementation of the iEL-SCF scheme within the LAMMPS molecular dynamics package.
• Utilizing two auxiliary variables for intermediate charges as an initial guess.
• Solving two sets of linear equations per time step to enforce charge conservation.
• Testing the scheme on systems including water, ferric hydroxide, nitramine RDX, and hexanitrostilbene.

Main Results:

• The iEL-SCF scheme successfully performs charge equilibration in ReaxFF simulations.
• A significant reduction in self-consistent field (SCF) cycles was observed, ranging from 50% to 80%.
• The efficiency gains were consistent across all tested diverse systems.

Conclusions:

• The iEL-SCF scheme offers a substantial computational speed-up for ReaxFF simulations.
• This improved efficiency facilitates larger and longer molecular dynamics simulations.
• The iEL-SCF method presents a valuable advancement for computational chemistry and materials science research.