Pymatgen

Pymatgen Materials Analysis

Systematic guidance for using pymatgen to analyze crystal structures, access materials databases, and interface with computational chemistry codes.

Pymatgen Workflow

1. Identify Task Type

What do you want to do?

Structure Creation/Loading:

• Create structure from scratch → references/core-objects.md
• Read from file (CIF, POSCAR, XYZ) → references/file-io.md
• Get from Materials Project → references/materials-project.md
• Generate from symmetry → references/structure-analysis.md

Structure Analysis:

• Analyze symmetry/space groups → references/structure-analysis.md
• Compare structures → references/structure-analysis.md
• Calculate properties → references/properties.md
• Visualize structures → references/visualization.md

Structure Manipulation:

• Create supercells/slabs → references/transformations.md
• Substitute atoms → references/transformations.md
• Apply symmetry operations → references/transformations.md
• Interpolate for NEB → references/transformations.md

Materials Database:

• Query Materials Project → references/materials-project.md
• Retrieve structures/properties → references/materials-project.md
• Build phase diagrams → references/phase-diagrams.md

Electronic Structure:

• Parse band structures → references/electronic-structure.md
• Plot DOS → references/electronic-structure.md
• Analyze VASP outputs → references/vasp-integration.md

Input Generation:

• Create VASP inputs → references/vasp-integration.md
• Generate Gaussian inputs → references/file-io.md
• Set up calculations → references/vasp-integration.md

2. Core Pymatgen Workflow

Basic pattern:

# 1. Import modules
from pymatgen.core import Structure, Lattice, Element

# 2. Load or create structure
structure = Structure.from_file("POSCAR")

# 3. Analyze or manipulate
print(f"Formula: {structure.composition.reduced_formula}")
print(f"Space group: {structure.get_space_group_info()}")

# 4. Transform if needed
supercell = structure * (2, 2, 1)  # 2x2x1 supercell

# 5. Write output
supercell.to(filename="POSCAR_supercell")

Quick Reference - Common Tasks

Load structure: Structure.from_file("file.cif") - Auto-detects format Create structure: See references/core-objects.md for Element, Lattice, Structure creation Analyze symmetry: SpacegroupAnalyzer(struct).get_space_group_symbol() Make supercell: structure * (2, 2, 1) or use transformations Query MP: MPRester(key).get_structure_by_material_id("mp-149") Generate VASP: MPRelaxSet(struct).write_input("dir") Plot bands/DOS: See references/electronic-structure.md

Detailed examples for all tasks in reference files.

Task Routing

Core Objects and Creation

Route to: references/core-objects.md

When:

• Creating structures from scratch
• Understanding Element, Site, Structure classes
• Working with Lattice objects
• Creating molecules
• Composition analysis

Key classes:

• Element, Species
• Lattice
• Site, PeriodicSite
• Structure, Molecule
• Composition

File Input/Output

Route to: references/file-io.md

When:

• Reading CIF, POSCAR, XYZ files
• Writing structures to files
• Format conversion
• Parsing calculation outputs
• Working with multiple formats

Supported formats:

• CIF (Crystallographic Information File)
• POSCAR/CONTCAR (VASP)
• XYZ (molecular coordinates)
• JSON (serialization)
• Many computational chemistry codes

Structure Analysis

Route to: references/structure-analysis.md

When:

• Finding space groups
• Symmetry operations
• Comparing structures
• Getting primitive/conventional cells
• Neighbor analysis

Key tools:

• SpacegroupAnalyzer
• StructureMatcher
• VoronoiAnalysis
• Distance calculations

Structure Transformations

Route to: references/transformations.md

When:

• Creating supercells
• Making slabs/surfaces
• Substituting elements
• Perturbing structures
• High-throughput workflows

Key modules:

• pymatgen.transformations.standard_transformations
• pymatgen.transformations.advanced_transformations
• pymatgen.alchemy

Materials Project API

Route to: references/materials-project.md

When:

• Querying materials database
• Getting structures by formula
• Retrieving calculated properties
• Accessing experimental data
• Building chemical systems

Key class:

• MPRester for API access
• Requires API key from materialsproject.org

Phase Diagrams

Route to: references/phase-diagrams.md

When:

• Constructing phase diagrams
• Analyzing stability
• Finding decomposition products
• Pourbaix diagrams
• Grand potential diagrams

Key classes:

• PhaseDiagram
• PhaseDiagramError (for stability analysis)
• PourbaixDiagram

Electronic Structure

Route to: references/electronic-structure.md

When:

• Analyzing band structures
• Plotting DOS
• Finding band gaps
• Analyzing orbital contributions
• Electronic property calculations

Key modules:

• pymatgen.electronic_structure.bandstructure
• pymatgen.electronic_structure.dos
• pymatgen.electronic_structure.plotter

VASP Integration

Route to: references/vasp-integration.md

When:

• Generating VASP inputs
• Parsing VASP outputs
• Creating input sets
• High-throughput VASP
• Custom INCAR settings

Key classes:

• MPRelaxSet, MPStaticSet, etc.
• Vasprun, Outcar parsers
• Poscar, Incar classes

Common Patterns

Pattern 1: Structure Analysis

• Load → Analyze composition/symmetry → Get primitive/conventional
• See examples/structure_analysis.py for complete workflow

Pattern 2: Materials Project to Calculation

• Query MP → Get structure → Generate VASP inputs → Customize settings
• See examples/mp_to_vasp.py

Pattern 3: High-Throughput Substitution

• Load base structure → Apply transformations → Write outputs
• See examples/substitution_study.py

Pattern 4: Electronic Structure Analysis

• Parse vasprun.xml → Extract band structure/DOS → Plot and analyze
• See examples/band_structure.py

All patterns detailed in examples/ directory with complete code.

Installation and Setup

Install Pymatgen

pip install pymatgen
# Or with optional dependencies
pip install pymatgen[all]

Configure Materials Project API

# Register at materialsproject.org to get API key
pmg config --add PMG_MAPI_KEY your_api_key_here

Set VASP Pseudopotential Path

pmg config --add PMG_VASP_PSP_DIR /path/to/vasp/potentials

Configuration File

Located at ~/.pmgrc.yaml:

PMG_MAPI_KEY: your_api_key_here
PMG_VASP_PSP_DIR: /path/to/vasp/potentials
PMG_DEFAULT_FUNCTIONAL: PBE

Common Issues and Solutions

Issue: Structure not defined

Problem: NameError: name 'Structure' is not defined

Solution:

from pymatgen.core import Structure

Issue: API key not working

Problem: MPRester returns authentication error

Solution:

1. Get API key from materialsproject.org (free account)
2. Configure: pmg config --add PMG_MAPI_KEY your_key
3. Or pass directly: MPRester("your_key")

Issue: POTCAR generation fails

Problem: Cannot write POTCAR files

Solution:

1. Set PSP directory: pmg config --add PMG_VASP_PSP_DIR /path
2. Ensure VASP pseudopotentials are properly installed
3. Check directory structure matches expected format

Issue: Import errors for optional dependencies

Problem: ImportError for plotting or specialized modules

Solution:

pip install pymatgen[all]  # Install all optional dependencies
# Or specific ones:
pip install matplotlib  # For plotting
pip install scipy      # For analysis tools

Best Practices

Object-Oriented Approach

• Use Structure/Molecule objects, not raw coordinates
• Leverage built-in methods (composition, symmetry, etc.)
• Chain operations for clarity

Serialization

• Use as_dict() / from_dict() for persistence
• Prefer JSON over pickle for code evolution
• Use MontyEncoder/MontyDecoder for complex objects

Transformations

• Use Transformation classes for reproducibility
• TransformedStructure tracks history
• Alchemy framework for high-throughput

Input Sets

• Use MPRelaxSet, MPStaticSet for standard calculations
• Customize by modifying Incar after creation
• Use InputGenerator for custom workflows

Materials Project

• Use context manager: with MPRester(...) as mpr:
• Batch queries when possible
• Cache results to avoid repeated API calls

Examples Directory

See examples/ for complete workflows:

• structure_analysis.py - Comprehensive structure analysis
• mp_query.py - Materials Project queries
• phase_diagram.py - Phase diagram construction
• band_structure.py - Electronic structure analysis
• vasp_workflow.py - VASP calculation setup
• substitution_study.py - High-throughput substitutions

Reference Documentation

• references/core-objects.md - Element, Structure, Lattice, Composition
• references/file-io.md - Reading/writing all file formats
• references/structure-analysis.md - Symmetry, comparison, neighbors
• references/transformations.md - Supercells, substitutions, perturbations
• references/materials-project.md - API usage and queries
• references/phase-diagrams.md - Phase diagram construction
• references/electronic-structure.md - Band structures and DOS
• references/vasp-integration.md - VASP input/output handling
• references/properties.md - Calculated properties
• references/visualization.md - Structure visualization

External Resources

• Official docs: https://pymatgen.org/
• Materials Project: https://materialsproject.org/
• GitHub: https://github.com/materialsproject/pymatgen
• Forum: https://matsci.org/pymatgen