Relativistic all-electron molecular dynamics simulations.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Molecular Dynamics

Background:

• Relativistic effects are crucial for accurate molecular simulations, especially for heavier elements.
• Implementing relativistic methods in molecular dynamics (MD) is computationally demanding.
• Existing MD packages often lack robust relativistic treatment.

Purpose of the Study:

• To implement the scalar-relativistic Douglas-Kroll-Hess (DKH) method within the CP2K simulation package.
• To validate the accuracy of relativistic gradients and molecular geometries.
• To investigate relativistic effects on the dynamics of hydrogen halide dimers.

Main Methods:

• Integration of the DKH method into the Born-Oppenheimer molecular dynamics framework of CP2K.
• Utilizing relativistic densities with a nonrelativistic gradient routine as a valid approximation.
• Performing first-principles molecular dynamics simulations on hydrogen halide dimers (HX)2, where X = F, Cl, Br, I.
• Evaluation of various electronic localization schemes.

Main Results:

• The DKH implementation shows excellent agreement with numerical gradients, with structural errors below 0.02 pm.
• Relativistic simulations of (HX)2 dimers reveal observable effects: increased amplitude of motion, decreased frequency, and elongated bond distances.
• Localization schemes exhibit small errors for equilibrium geometries but larger errors for compressed configurations.

Conclusions:

• The scalar-relativistic DKH method is successfully implemented in CP2K for Born-Oppenheimer molecular dynamics.
• The approximation of using relativistic densities in nonrelativistic gradients is validated.
• Relativistic effects significantly influence molecular dynamics, particularly for systems with heavier halogens.