Fragment Molecular Orbital Molecular Dynamics with the Fully Analytic Energy Gradient

Area of Science:

• Computational chemistry
• Molecular dynamics simulations
• Quantum chemistry

Background:

• Fragment molecular orbital (FMO) methods are used for large molecular systems.
• Previous FMO-MD simulations of liquid water employed approximate energy gradients.
• Accurate energy conservation is crucial for reliable molecular dynamics simulations.

Purpose of the Study:

• To investigate the impact of a fully analytic energy gradient on FMO-MD simulations of liquid water.
• To compare the performance of FMO-MD with analytic versus approximate energy gradients.
• To evaluate the role of two-body versus three-body corrections in FMO-MD.

Main Methods:

• Fragment molecular orbital molecular dynamics (FMO-MD) with periodic boundary conditions.
• Utilized a fully analytic energy gradient, including response terms.
• Employed electrostatic potential point charge and electrostatic dimer approximations.
• Performed simulations with FMO2 (two-body corrections) and compared with FMO3 (three-body corrections).

Main Results:

• The fully analytic energy gradient significantly improved energy conservation in the NVE ensemble for liquid water.
• FMO-MD with the analytic gradient and FMO2 corrections showed better energy conservation than previous FMO-MD simulations using approximate gradients and FMO3 corrections.
• Inclusion of response terms in the analytic gradient was key to enhanced energy conservation.

Conclusions:

• A fully analytic energy gradient is essential for accurate FMO-MD simulations of liquid water.
• FMO-MD with analytic gradients offers superior energy conservation compared to simulations with approximate gradients.
• The FMO2 approach with an analytic gradient provides a more accurate and efficient simulation of liquid water.