Simplify Coarse-Grained Molecular Modeling with GROMACS Wizard

Coarse-grained (CG) molecular modeling is a popular approach in molecular design for studying complex systems while reducing computational costs. However, efficiently preparing a coarse-grained system can feel daunting, even for experienced molecular modelers. The GROMACS Wizard in the SAMSON platform offers a streamlined solution, providing clear steps to prepare, solvate, and neutralize CG systems for downstream molecular dynamics (MD) simulations.

The Pain Point: Preparing Coarse-Grained Systems

Preparing a CG system involves generating structure and topology files, defining a periodic box, solvating the system, and adding ions, all while ensuring compatibility with the selected force field. Missing a step or incorrectly setting parameters can lead to failed simulations or inaccurate results. This blog post walks you through this process using GROMACS Wizard, focusing on the Preparation step, starting from CG files generated with Martinize2.

Step-by-Step Guide to Prepare Your CG System

  1. Launch the Prepare Tab: Begin in the Prepare tab of GROMACS Wizard. In the Set system section, choose Folder as the source.
  2. Select Input Files: Click Browse… to select a folder containing the required CG model data, including structure (.pdb) and topology (.top) files. Make sure your folder includes outputs from Martinize2, such as *_CG.pdb and *_CG.top. Once selected, the system displays a list of detected input files, ensuring you have everything needed.
  3. Load the System: Load the detected .pdb file by clicking the Load button. The system will compute a periodic box, critical for simulations. GROMACS Wizard visualizes this step clearly:

    Computed periodic box

  4. Set the Force Field: If you used Martinize2 for the CG model, GROMACS Wizard automatically sets the force field to martini_v.3.0.0 and the solvent model to Martini water. Ensure these settings are accurate:

    Choose MARTINI v.3.0.0 force field

  5. Customize Solvent Settings: Enable the Add solvent option to solvate the system. Adjust parameters in the pop-up solvent options window by increasing the default van der Waals distance (e.g., to 0.21 nm) to ensure proper CG bead spacing:

    Solvent options

  6. Adjust the Periodic Box: You can modify the box size as needed, ensuring a minimum 1 nm distance between images. Consider switching the unit cell to Rhombic dodecahedron for optimal packing.
  7. Add Ions: Neutralize the system by replacing solvent molecules with ions. You can also set specific salt concentrations for your simulation. Make sure you activate the option to add solvent before adding ions:

    Add ions - Salt concentration

  8. Finalize the Preparation: Once all parameters are set, click the Prepare button. You can choose to inspect the prepared structure or proceed directly to minimization, equilibration, and production MD simulations.

Why Use GROMACS Wizard in SAMSON?

With GROMACS Wizard, the process of preparing CG systems becomes straightforward and efficient. Instead of struggling with command-line tools or manual configurations, this guided interface minimizes errors and saves time, empowering researchers to focus on their molecular modeling tasks.

To explore the full documentation detailing coarse-grained system preparation, visit this page.

Note: SAMSON and all SAMSON Extensions are free for non-commercial use. Get SAMSON at https://www.samson-connect.net.

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