MCP Materials Server

Instructions

Implementation Reference

• src/mcp_materials/server.py:470-544 (handler)

  The get_phase_diagram tool handler: fetches phase diagram entries from Materials Project API, constructs PhaseDiagram using pymatgen, and returns JSON with stable/unstable phases, formation energies, and decomposition info.
  @mcp.tool() def get_phase_diagram( elements: list[str], ) -> str: """ Get phase diagram data for a chemical system. Args: elements: List of elements defining the system (e.g., ["Li", "Fe", "O"] for Li-Fe-O system) Returns: JSON with phase diagram entries including stable phases, formation energies, and decomposition products """ has_key, key_or_error = check_api_key() if not has_key: return json.dumps({"error": key_or_error}) try: from mp_api.client import MPRester from pymatgen.analysis.phase_diagram import PhaseDiagram with MPRester(key_or_error) as mpr: # Get all entries in the chemical system chemsys = "-".join(sorted(elements)) entries = mpr.get_entries_in_chemsys(elements) if not entries: return json.dumps({ "error": f"No entries found for chemical system: {chemsys}", "chemical_system": chemsys, }) # Build phase diagram pd = PhaseDiagram(entries) # Get stable entries stable_entries = [] for entry in pd.stable_entries: stable_entries.append({ "material_id": str(entry.entry_id) if hasattr(entry, 'entry_id') else None, "formula": entry.composition.reduced_formula, "energy_per_atom_eV": entry.energy_per_atom, "formation_energy_per_atom_eV": pd.get_form_energy_per_atom(entry), }) # Get unstable entries with decomposition info unstable_entries = [] for entry in pd.unstable_entries: decomp, e_above_hull = pd.get_decomp_and_e_above_hull(entry) decomp_products = [p.composition.reduced_formula for p in decomp.keys()] unstable_entries.append({ "material_id": str(entry.entry_id) if hasattr(entry, 'entry_id') else None, "formula": entry.composition.reduced_formula, "energy_above_hull_eV": e_above_hull, "decomposes_to": decomp_products, }) return json.dumps({ "chemical_system": chemsys, "num_elements": len(elements), "total_entries": len(entries), "stable_phases": { "count": len(stable_entries), "entries": stable_entries, }, "unstable_phases": { "count": len(unstable_entries), "entries": unstable_entries[:20], # Limit to first 20 }, }, indent=2) except ImportError: return json.dumps({"error": "mp-api or pymatgen not installed"}) except Exception as e: return json.dumps({"error": str(e)})
• src/mcp_materials/server.py:470-470 (registration)

  MCP tool registration decorator for get_phase_diagram.
  @mcp.tool()
• src/mcp_materials/server.py:471-481 (schema)

  Input schema defined by function signature (elements: list[str]) and comprehensive docstring describing args and return format.
  def get_phase_diagram( elements: list[str], ) -> str: """ Get phase diagram data for a chemical system. Args: elements: List of elements defining the system (e.g., ["Li", "Fe", "O"] for Li-Fe-O system) Returns: JSON with phase diagram entries including stable phases, formation energies, and decomposition products