Evidence class: synthetic-only. This fixture uses invented signed uniaxial strain and stress rows in one declared component convention. It verifies a least-squares slope, signed-strain symmetry, and the cubic stability inequalities for the invented matrix. It does not calculate a stress tensor or infer a material response.
Do not use this page as the first step of an elastic calculation. Start with a real reference cell, inspect named positive and negative strained structures in VESTA or ASE, and read energies, all stress components, residual forces, and internal-relaxation status from the selected calculator output. Return here only if the remaining problem is understanding the arithmetic of a signed fit.
Optional toy after inspecting real strained cells
This page has no reference crystal, stress output, or material-specific symmetry decision. Plot the real energy and stress series before fitting; the electronic-property and response resources provide routes for producing those objects.
Optional replay of the invented ledger
python3 examples/practical-guides/strain_stress_ledger.py \
--svg public/media/practical-guides/elastic-constants-and-mechanical-properties/check-strain-stress-ledger/strain-stress-ledger.svgIf the synthetic positive and negative rows fail to close, inspect the printed row table and units in the terminal; that diagnoses this toy only. In a material workflow, asymmetry or a poor residual sends the researcher back to the corresponding real deformed structure and stress output, not to this script.
Nielsen and Martin provide the stress formalism. Mouhat and Coudert summarize symmetry-specific elastic-stability conditions, and VASP’s finite-difference documentation distinguishes clamped and ion-relaxed moduli.
What this guide verifies
Execution verifies invented ledger arithmetic, an explicit units label, signed-strain fit closure, the selected cubic inequalities, and original SVG rendering. It does not converge stress, calculate elastic constants for any material, validate a crystal class, establish mechanical or dynamical stability, predict strength or fracture, or establish a scientific conclusion.