Equation Of States Utility

Equation of state (EOS) utilities.

This module centralizes common equation-of-state formulas used across ReaxKit. Currently includes Vinet EOS in two forms:

1) Energy–volume form in eV (used for fitting E(V) from fort.99/fort.74). 2) Legacy "trainset" form matching the translated Fortran elastic_energy_v2 generator.

Notes

• The two Vinet implementations use different parameterizations/units, so they are conceptually related but not drop-in replacements for each other.
• Explanation for the Rose–Vinet equation of state can be found here: doi:10.1029/JB092iB09p09319

vinet_energy_ev(V, E0, K0_eV_A3, V0, C)

Vinet EOS: energy–volume form (eV, eV/Å^3).

Parameters:

Name	Type	Description	Default
V	ndarray	Volume(s) (Å^3).	required
E0	float	Equilibrium energy (eV).	required
K0_eV_A3	float	Bulk modulus at equilibrium (eV/Å^3).	required
V0	float	Equilibrium volume (Å^3).	required
C	float	Vinet shape parameter (dimensionless).	required

Returns:

Type	Description
ndarray	Energy at each volume V (eV).

vinet_energy_trainset(*, volume, reference_volume, bulk_modulus_gpa, bulk_modulus_pressure_derivative, reference_energy=0.0, energy_conversion_factor)

Vinet EOS: legacy trainset-generator form.

This matches your translated Fortran elastic_energy_v2 bulk block logic. It returns energies in the generator's legacy energy units.

Parameters:

Name	Type	Description	Default
volume	float	Current volume V (Å^3).	required
reference_volume	float	Reference volume V0 (Å^3).	required
bulk_modulus_gpa	float	Bulk modulus B0 (GPa).	required
bulk_modulus_pressure_derivative	float	Pressure derivative B0' (dimensionless).	required
reference_energy	float	Reference energy offset E0 (legacy units).	0.0
energy_conversion_factor	float	The generator's conversion factor (the one you currently call ENERGY_CONVERSION_FACTOR).	required

Returns:

Type	Description
float	EOS energy in the generator's legacy energy units.