E-CAM Case Study: The development of the GC-AdResS scheme:

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from smooth coupling

to a direct interface (abrupt)

Dr. Christian Krekeler, Freie Universität Berlin

Abstract

GC-AdResS is a technique  that speeds up computations without loss of accuracy for key system properties by dividing the simulation box into two or more regions having different levels of resolution, for instance a high resolution region where the molecules of the system are treated at an atomistic level of detail, and other regions where molecules are treated at a coarse grained level, and transition regions where a weighted average of the two resolutions is used. The goal of the E-CAM GC-AdResS pilot project was to eliminate  the need of a transition region so as to significantly improve  performance, and to allow much greater flexibility. For example, the  low resolution region can be a particle reservoir (ranging in detail from coarse grained  to ideal gas particles) and a high resolution atomistic region with no transition region, as was needed hitherto.  The only requirement is that the two regions can exchange particles, and that a corresponding “thermodynamic” force is computed self-consistently, which it turns out is very simple to implement.

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Abrupt GC-AdResS: A new and more general implementation of the Grand Canonical Adaptive Resolution Scheme (GC-AdResS)

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The Grand Canonical Adaptive resolution scheme (GC-AdResS) gives a methodological description to partition a simulation box into different regions with different degrees of accuracy. For more details on the theory see Refs. [1,2,3].

In the context of an E-CAM pilot project focused on the development of the GC-AdResS scheme, an updated version of GC-AdResS was built and implemented in GROMACS, as reported in https://aip.scitation.org/doi/10.1063/1.5031206 (open access version: https://arxiv.org/abs/1806.09870). The main goal of the project is to develop a library or recipe with which GC-AdResS can be implemented in any Classical MD Code.

The current implementation of GC- AdResS in GROMACS has several performance problems. We know that the main performance loss of AdResS simulations in GROMACS is in the neighbouring list search and the generic serial force calculation linking the atomistic (AT) and coarse grained (CG) forces together via a smooth weighting function. Thus, to remove the bottleneck with respect to performance and a hindrance regarding the easy/general implementation into other codes and eliminate the non optimized force calculation, we had to change the neighbourlist search. This lead to a considerable speed up of the code. Furthermore it decouples the method directly from the core of any MD code, which does not hinder the performance and makes the scheme hardware independent[4].

This module presents a very straight forward way to implement a new partitioning scheme in GROMACS . And this solves two problems which affect the performance, the neighborlist search and the generic force kernel.

Information about module purpose, background information, software installation, testing and a link to the source code, can be found in our E-CAM software Library here.

E-CAM Deliverables D4.3[5] and D4.4[6] present more modules developed in the context of this pilot project.

References

[1] L. Delle Site and M. Praprotnik, “Molecular Systems with Open Boundaries: Theory and Simulation,” Phys. Rep., vol. 693, pp. 1–56, 2017

[2] H.Wang, C. Schütte, and L.Delle Site, “Adaptive Resolution Simulation (AdResS): A Smooth Thermodynamic and Structural Transition fromAtomistic to Coarse Grained Resolution and Vice Versa in a Grand Canonical Fashion,” J. Chem. Theory Comput., vol. 8, pp. 2878–2887, 2012

[3] H. Wang, C. Hartmann, C. Schütte, and L. Delle Site, “Grand-Canonical-Like Molecular-Dynamics Simulations by Using an Adaptive-Resolution Technique,” Phys. Rev. X, vol. 3, p. 011018, 2013

[4] C. Krekeler, A. Agarwal, C. Junghans, M. Prapotnik and L. Delle Site, “Adaptive resolution molecular dynamics technique: Down to the essential”, J. Chem. Phys. 149, 024104

[5] B. Duenweg, J. Castagna, S. Chiacchera, H. Kobayashi, and C. Krekeler, “D4.3: Meso– and multi–scale modelling E-CAM modules II”, March 2018 . [Online]. Available: https://doi.org/10.5281/zenodo.1210075

[6] B. Duenweg, J. Castagna, S. Chiacchera, and C. Krekeler, “D4.4: Meso– and multi–scale modelling E-CAM modules III”, Jan 2019 . [Online]. Available: https://doi.org/10.5281/zenodo.2555012

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E-CAM related work labeled as “Excellent Science” by the EC Innovation Radar Initiative

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The Innovation Radar aims to identify high-potential innovations and innovators. It is an important source of actionable intelligence on innovations emerging from research and innovation projects funded through European Union programmes.

E-CAM is associated to the following Innovations (Innovation topic: excellence science):

    1. Improved Simulation Software Packages for Molecular Dynamics (see link)
    2. Improved software modules for Meso– and multi–scale modelling (see link)

Related to the work of our E-CAM funded Postdoctoral researchers supervised by scientists in the team, working on:

  • Development of the OpenPathSampling package to study rare events  (Universiteit van Amsterdam). Link1
  • Implementation of GPU version of DL_MESO_DPD (Hartree Centre (STFC)). Link
  • Development of polarizable mesoscale model for DL_MESO_DPD (Hartree Centre (STFC)). Link

  • Development of the GC-AdResS scheme (Freie Universitaet Berlin). Link

  • Implementation of hierarchical strategy on ESPResSO++ (Max Plank Institute for Polymer Research, Mainz). Link
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New E-CAM publication is out: “Molecular Dynamics of Open Systems: Construction of a Mean‐Field Particle Reservoir”

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New publication from E-CAM partners working at the Institute of Mathematics of the Freie Universität Berlin:

Molecular Dynamics of Open Systems: Construction of a Mean‐Field Particle Reservoir

Authors: Luigi Delle Site, Christian Krekeler, John Whittaker, Animesh Agarwal, Rupert Klein, and Felix Höfling

Adv. Theory Simul. 2019, 1900014, DOI: 10.1002/adts.201900014 (Open access)

Synopsis

A procedure for the construction of a particle and energy reservoir for the simulation of open molecular systems is presented. The reservoir is made of non‐interacting particles (tracers), embedded in a mean‐field. The tracer molecules acquire atomistic resolution upon entering the atomistic region, while atomistic molecules become tracers after crossing the atomistic boundary.

Abstract

The simulation of open molecular systems requires explicit or implicit reservoirs of energy and particles. Whereas full atomistic resolution is desired in the region of interest, there is some freedom in the implementation of the reservoirs. Here, a combined, explicit reservoir is constructed by interfacing the atomistic region with regions of point-like, non-interacting particles (tracers) embedded in a thermodynamic mean field. The tracer molecules acquire atomistic resolution upon entering the atomistic region and equilibrate with this environment, while atomistic molecules become tracers governed by an effective mean-field potential after crossing the atomistic boundary. The approach is extensively tested on thermodynamic, structural, and dynamic properties of liquid water. Conceptual and numerical advantages of the procedure as well as new perspectives are highlighted and discussed.

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New publication is out: “Adaptive Resolution Molecular Dynamics Technique: Down to the Essential”

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A new publication by the Theoretical and Mathematical Physics in Molecular Simulation group of the Freie Universität Berlin, lead by Prof. Luigi Delle Site, E-CAM partner, was published in the Journal of Chemical Physics. In it, the authors study the application of the thermodynamic force in the coupling region of an adaptive resolution molecular dynamics simulation (AdResS) approach which assures thermodynamic equilibrium and proper exchange of molecules between atomistically resolved and coarse-grained regions.

The publication post-print version is open access and can be downloaded directly from the Zenodo repository here. The publisher AIP version can be found at https://doi.org/10.1063/1.5031206.

This work was performed in the context of the E-CAM pilot project on the development of the GC-AdResS scheme, which is a collaboration with MODAL AG. One of its goals is to develop a library or recipe with which GC-AdResS can be implemented in any MD Code. The current focus is to adjust the implemented version of GC-AdResS in GROMACS. The long-term goal of this project is to promote and stimulate the community to use it as a tool for multiscale simulations and analysis. More information about this pilot project can be found here.

Article

Title: Adaptive Resolution Molecular Dynamics Technique: Down to the Essential

Authors: Christian Krekeler, Animesh Agarwal, Christoph Junghans, Matej Praprotnik, Luigi Delle Site

Abstract: We investigate the role of the thermodynamic (TD) force, as an essential and sufficient technical ingredient for an efficient and accurate adaptive resolution algorithm. Such a force applied in the coupling region of an adaptive resolution Molecular Dynamics (MD) set-up, assures thermodynamic equilibrium between atomistically resolved and coarse-grained regions, allowing the proper exchange of molecules. We numerically prove that indeed for systems as relevant as liquid water and 1,3-dimethylimidazolium chloride ionic liquid, the combined action of the TD force and thermostat allows for computationally efficient and numerically accurate simulations, beyond the current capabilities of adaptive resolution set-ups, which employ switching functions in the coupling region.

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New publication using the GC-AdResS molecular dynamics technique

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The publication “Probing spatial locality in ionic liquids with the grand canonical adaptive resolution molecular dynamics technique (GC-AdResS)“ by the Theoretical and Mathematical Physics in Molecular Simulation group of the Freie Universität Berlin, lead by Prof.Luigi Delle Site, E-CAM partner, describes the use of the GC-AdResS molecular dynamics technique to test the spatial locality of the ionic liquid 1-ethyl 3-methyl imidazolium chloride liquid. The main aspect of GC-AdResS is the possibility to couple two simulation boxes together and combine the advantages of classical atomistic simulations with those from coarse gained simulations.

The publication post-print version is open access and can be downloaded directly from the Zenodo repository here. The publisher AIP version can be found at http://aip.scitation.org/doi/10.1063/1.5009066.

E-CAM currently runs a pilot project on the development of the GC-AdResS scheme and one of its goals is to develop a library or recipe with which GC-AdResS can be implemented in any MD Code. The current focus is to adjust the implemented version of GC-AdResS in GROMACS. The long-term goal of this project is to promote and stimulate the community to use it as a tool for multiscale simulations and analysis. More information about this pilot project can be found here.

Article

Title: Probing spatial locality in ionic liquids with the grand canonical adaptive resolution molecular dynamics technique

Authors:  B. Shadrack Jabes, C. Krekeler, R. Klein and L. Delle Site

Abstract: We employ the Grand Canonical Adaptive Resolution Simulation (GC-AdResS) molecular dynamics technique to test the spatial locality of the 1-ethyl 3-methyl imidazolium chloride liquid. In GC-AdResS, atomistic details are kept only in an open sub-region of the system while the environment is treated at coarse-grained level; thus, if spatial quantities calculated in such a sub-region agree with the equivalent quantities calculated in a full atomistic simulation, then the atomistic degrees of freedom outside the sub-region play a negligible role. The size of the sub-region fixes the degree of spatial locality of a certain quantity. We show that even for sub-regions whose radius corresponds to the size of a few molecules, spatial properties are reasonably reproduced thus suggesting a higher degree of spatial locality, a hypothesis put forward also by other researchers and that seems to play an important role for the characterization of fundamental properties of a large class of ionic liquids.

The Journal of Chemical Physics 148, 193804 (2018)
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