Geometric integration in extended lagrangian self consistent tight-binding molecular dynamics
(English)Article in journal (Other academic) Submitted
Geometric integration schemes for extended Lagrangian self-consistent tight-binding molecular dynamics, including a weak dissipation to remove numerical noise, are developed and analyzed. The extended Lagrangian framework enables the geometric integration of both the nuclear andelectronic degrees of freedom. This provides highly effcient simulations that are stable and energy conserving even under incomplete and approximate self-consistent field (SCF) convergence. We investigate three different geometric integration schemes: i) regular time reversible Verlet, ii) secondorder optimal symplectic, and iii) third order optimal symplectic. We look at energy conservation, accuracy and stabilitty as a function of dissipation, integration time step, and SCF convergence. We find that the inclusion of dissipation in the symplectic integration methods gives an efficient damping of numerical noise or perturbations that otherwise may accumulate from finite arithmetics in a perfect reversible dynamics. The modification of the integration breakes symplecticity and introduces a global energy drift. The systematic drift in energy and the broken symplecticity can be kept arbitrarily small without significant perturbations of the molecular trajectories. However, we have yet to find a formalism for the inclusion of the dissipation in higher-order symplectic integration methods with a more optimal balance between efficient damping and minimal global energy drift.
Other Physics Topics Condensed Matter Physics
IdentifiersURN: urn:nbn:se:kth:diva-26959OAI: oai:DiVA.org:kth-26959DiVA: diva2:373164
QC 201012022010-12-022010-11-302010-12-02Bibliographically approved