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Unit for Young's modulus #4435

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#4436
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Unit for Young's modulus#4435
#4436
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@anyangml

Description

@anyangml
anyangml
opened on Jun 12, 2025

Python version

3.11.5

Pymatgen version

2025.5.28

Operating system version

No response

Current behavior

I think the unit for Young's modulus is wrong.

If I understand correctly, in the following calculation, the units for shear modulus and bulk modulus are assumed to be GPa.

pymatgen/src/pymatgen/analysis/elasticity/elastic.py

Lines 199 to 205 in 20afc86

def y_mod(self) -> float:
"""
Calculates Young's modulus (in SI units) using the
Voigt-Reuss-Hill averages of bulk and shear moduli.
"""
return 9.0e9 * self.k_vrh * self.g_vrh / (3 * self.k_vrh + self.g_vrh)

However the units are in eV/A^3

pymatgen/src/pymatgen/analysis/elasticity/elastic.py

Lines 188 to 198 in 20afc86

@property
def k_vrh(self) -> float:
"""The K_vrh (Voigt-Reuss-Hill) average bulk modulus (in eV/A^3)."""
return 0.5 * (self.k_voigt + self.k_reuss)
@property
def g_vrh(self) -> float:
"""The G_vrh (Voigt-Reuss-Hill) average shear modulus (in eV/A^3)."""
return 0.5 * (self.g_voigt + self.g_reuss)
@property

Expected Behavior

a unit conversion from eV/A^3 to GPa shall be applied before calculating Young's modulus

Minimal example



Relevant files to reproduce this bug


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