mat-elasticity

Elastic Tensor Skill

This skill calculates the full elastic tensor ($C_{ij}$) and derived mechanical properties of crystalline materials using Machine Learning Interatomic Potentials (MLIPs). It applies a set of normal and shear strains, computes the resulting stresses, and fits the elastic constants via least-squares regression using MatCalc's ElasticityCalc.

Goal

Calculate the elastic tensor ($C_{ij}$) of a material by applying systematic deformations (normal and shear strains), computing the stress response with an MLIP, and extracting the full Voigt elastic tensor along with:

• Bulk modulus $B$ (Voigt-Reuss-Hill average)
• Shear modulus $G$ (Voigt-Reuss-Hill average)
• Young's modulus $E$
• Poisson's ratio $\nu$

1. Prerequisites

• The appropriate MLIP wrapper must be available (MACEWrapper, MatGLWrapper, or FAIRCHEMWrapper).
• matcalc must be installed in the relevant conda environment.
• A structure file (CIF, POSCAR, or other ASE-readable format). The structure will be relaxed before deformation by default.

2. Choosing a Foundation Potential

Elastic tensor calculations require accurate stress predictions across multiple deformed structures.

[!IMPORTANT]

• Use OMAT or MatPES trained models: These models (e.g., MACE-OMAT-0-small, CHGNet-MatPES-PBE, TensorNet-MatPES-r2SCAN) are trained with stress labels and provide reliable stress predictions.
• Stress accuracy is critical: Unlike EOS (which only uses energies), elasticity calculations directly depend on stress tensors. Models trained without stress labels may give poor results.

Refer to the foundation-potentials skill for more details.

3. Calculation Workflow

To calculate the elastic tensor, use the calculate_elasticity.py script:

# Env: mace-agent
python .agents/skills/mat-elasticity/scripts/calculate_elasticity.py \
    --structure path/to/structure.cif \
    --model_type mace \
    --model_name MACE-OMAT-0-small \
    --norm_strains -0.01 -0.005 0.005 0.01 \
    --shear_strains -0.06 -0.03 0.03 0.06 \
    --relax_structure \
    --output_dir research/my_folder/elasticity