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Hitchhiker's guide to second-generation Car-Parrinello ab-initio molecular dynamics

Thomas D. Kühne

TL;DR

The paper addresses reliable Born-Oppenheimer AIMD with second-generation CP2G by detailing a practical workflow that starts from BOMD pre-equilibration, optimizes density-matrix propagation via an appropriate corrector-step size and ASPC order, and completes with a carefully tuned modified Langevin dynamics to recover correct Boltzmann sampling. The approach combines fixed-density-matrix relaxation, energy-dissipation monitoring, and bootstrapping of $\gamma_{D}$ and overlay noise $\gamma_{L}$, including optional per-species friction and concurrent relaxation of electronic and nuclear degrees of freedom, implemented in CP2K/Quickstep. Its key contributions are a concrete parameter-tuning protocol, explicit guidance on exploration runs, and demonstrations on liquid water, enabling practical, accurate CP2G AIMD with controlled sampling. The work offers a usable route to BO-like sampling for ab initio liquids and related systems, balancing accuracy, stability, and computational efficiency.

Abstract

In a recent letter [T. D. Kühne, M. Krack, F. Mohamed and M. Parrinello, Phys. Rev. Lett. 98, 066401 (2007)], we outlined a new Car-Parrinello-like approach to Born-Oppenheimer molecular dynamics. Here, we provide a guide to performing actual calculations using our method and demonstrate this on liquid water at ambient conditions. We do not go into methodological details beyond those necessary for applying this approach, but focus on practical details pertinent to our particular implementation within the CP2K/Quickstep code [T. D. Kühne et al., J. Chem. Phys. 152, 194103 (2020)].

Hitchhiker's guide to second-generation Car-Parrinello ab-initio molecular dynamics

TL;DR

The paper addresses reliable Born-Oppenheimer AIMD with second-generation CP2G by detailing a practical workflow that starts from BOMD pre-equilibration, optimizes density-matrix propagation via an appropriate corrector-step size and ASPC order, and completes with a carefully tuned modified Langevin dynamics to recover correct Boltzmann sampling. The approach combines fixed-density-matrix relaxation, energy-dissipation monitoring, and bootstrapping of and overlay noise , including optional per-species friction and concurrent relaxation of electronic and nuclear degrees of freedom, implemented in CP2K/Quickstep. Its key contributions are a concrete parameter-tuning protocol, explicit guidance on exploration runs, and demonstrations on liquid water, enabling practical, accurate CP2G AIMD with controlled sampling. The work offers a usable route to BO-like sampling for ab initio liquids and related systems, balancing accuracy, stability, and computational efficiency.

Abstract

In a recent letter [T. D. Kühne, M. Krack, F. Mohamed and M. Parrinello, Phys. Rev. Lett. 98, 066401 (2007)], we outlined a new Car-Parrinello-like approach to Born-Oppenheimer molecular dynamics. Here, we provide a guide to performing actual calculations using our method and demonstrate this on liquid water at ambient conditions. We do not go into methodological details beyond those necessary for applying this approach, but focus on practical details pertinent to our particular implementation within the CP2K/Quickstep code [T. D. Kühne et al., J. Chem. Phys. 152, 194103 (2020)].
Paper Structure (12 sections, 12 figures)

This paper contains 12 sections, 12 figures.

Table of Contents

  1. Introduction
  2. PART 0: Born-Oppenheimer Molecular Dynamics-based Pre-Equilibration
  3. Part I: Optimizing the Density Matrix Propagation
  4. Identification of the Best Corrector Step Size
  5. Determination of the ASPC Propagation Order
  6. Final Relaxation
  7. Part II: Tuning the Modified Langevin Equation to Ensure Accurate Sampling
  8. Determine $\gamma_{D}$ by Bootstrapping
  9. Adding Overlay Noise to Ensure a Correct Sampling of the Boltzmann Distribution
  10. Atomic Species-Dependent Gamma Values
  11. Concurrent Relaxation of nuclear and electronic degrees of freedom
  12. The applied GTH-PPs and Gaussian basis-sets

Figures (12)

  • Figure 1: Nuclear temperature as a function of time during the BOMD-based pre-equilibration.
  • Figure 2: Corrector step size determination
  • Figure 3: Energy evolution with respect to the ASPC order
  • Figure 4: Final Relaxation using the fast method
  • Figure 5: Coarse-grained $\gamma_{D}$ search
  • ...and 7 more figures