mat-melting-point

Melting Point

Goal

To determine the thermodynamic melting temperature ($T_m$) of a bulk material by equilibrating a solid-liquid interface in an NVE ensemble.

Instructions

1. Background Research:

   • Search for the approximate melting point ($T_m$) and boiling/evaporation point ($T_{vap}$) of the material.
   • Choose a melting temperature $T_{melt}$ where $T_m < T_{melt} \ll T_{vap}$.
   • MD Parameters: Refer to the mat-md-monitors skill for best practices on timesteps and monitors. In general, use a 2.0 fs timestep for systems without Hydrogen.

2. Phase Preparation:

   • Solid: Create a supercell using create_supercell.py.

   # Env: base-agent
   python .agents/skills/mat-melting-point/scripts/create_supercell.py [input_structure.cif] [solid_supercell.cif] --min_length 20.0
   

   • Liquid: Melt a block using 1D-NPT (with mask) to ensure matching dimensions.

   mcp_mace_run_md(
       structure_data="solid_supercell.cif",
       temperature=2000,  # REPLACE with T_melt from Step 1
       ensemble="npt",
       steps=5000,
       timestep=2.0,      # Use 2.0 fs for most inorganic systems
       pressure=1.0,      # Apply positive pressure (1-2 bar) to prevent evaporation
       pressure_mask=[1, 0, 0], # REQUIRED: Must match the stacking axis (e.g., x-axis)
       output_dir="melt_stage"
   )
   

   • Visual Inspection (CRITICAL): Sometimes the cell does not fully melt within the specified MD steps. You MUST use the mcp_base_visualize_structure tool to generate an image of the final liquid.cif structure (or trajectory) and have the VLM visually inspect the image to confirm that the long-range crystalline order has been destroyed and the cell is completely melted. If it has not, you must run the MD with a higher temperature or for more steps.

3. Interface Creation: Use create_interface.py to concatenate the two phases.

   # Env: base-agent
   python .agents/skills/mat-melting-point/scripts/create_interface.py solid.cif liquid.cif --axis 0 --output interface.cif
   

4. Relaxation: Perform an ionic relaxation using the relax_structure MCP tool with relax_cell=True. This allows the unit cell to adjust (shrink/expand) to match the density, and remove the interface energy created by stacking the two cells.

   mcp_mace_relax_structure(structure_data="interface.cif", relax_cell=True)
   

5. Phase Verification: Before running production MD, verify solid-liquid coexistence in all structures.