BJP Potential (Bouhadja)¶

The BJP potential, developed by Bouhadja et al., is a Born-Mayer-Huggins (BMH) force field specifically parameterized for calcium aluminosilicate (CAS) glass systems. It provides accurate structural and thermodynamic properties for Ca-Al-Si-O compositions.

Reference¶

Y. Bouhadja, N. Jakse, A. Pasturel. "Structural and dynamic properties of calcium aluminosilicate melts: a molecular dynamics study", J. Chem. Phys. 138, 224510 (2013). DOI:10.1063/1.4809523

Functional Form¶

The total pairwise interaction energy uses the Born-Mayer-Huggins form:

\[ V(r_{ij}) = A_{ij} \, e^{-r_{ij}/\rho_{ij}} - \frac{C_{ij}}{r_{ij}^6} + \frac{D_{ij}}{r_{ij}^8} + \frac{q_i q_j}{r_{ij}} \]

where:

Symbol	Description
\(A_{ij}\)	Repulsion energy prefactor (eV)
\(\rho_{ij}\)	Repulsion range parameter (Å)
\(C_{ij}\)	Van der Waals attraction coefficient (eV·Å⁶)
\(D_{ij}\)	Dipole-quadrupole correction coefficient (eV·Å⁸)
\(q_i, q_j\)	Partial atomic charges

The Coulomb interactions are handled within the LAMMPS born/coul/dsf pair style with a DSF damping parameter of 0.25 Å⁻¹ and a cutoff of 8.0 Å.

LAMMPS pair style: born/coul/dsf 0.25 8.0

Charges¶

All charges are fixed at:

Element	Charge (\(e\))
O	−1.2
Ca	+1.2
Al	+1.8
Si	+2.4

Note: These are the same partial charges as in the PMMCS potential, consistent with the factor-of-0.6 scaling from formal charges.

Supported Elements¶

BJP supports a focused set of 4 elements:

Element	Role in glass
Si	Network former
Al	Network former / intermediate
Ca	Network modifier
O	Anion

This makes BJP specifically designed for CAS glasses such as: - Anorthite (CaAl₂Si₂O₈) - Gehlenite (Ca₂Al₂SiO₇) - Wollastonite (CaSiO₃) - General Ca-Al-Si-O compositions

Usage¶

from amorphouspy import get_structure_dict, generate_potential

# BJP works only with Ca-Al-Si-O compositions
structure_dict = get_structure_dict(
    {"CaO": 0.25, "Al2O3": 0.25, "SiO2": 0.5},
    target_atoms=3000,
)

potential = generate_potential(structure_dict, potential_type="bjp")

What the generator produces¶

The BJP generator creates LAMMPS configuration lines that: 1. Define the born/coul/dsf pair style (BMH + DSF Coulomb in one style) 2. Set atomic charges 3. Define BMH parameters (\(A\), \(\rho\), \(\sigma\), \(C\), \(D\)) for all pair interactions

Technical Details¶

Born-Mayer-Huggins vs. Buckingham¶

The BMH form used by BJP differs from the standard Buckingham potential in two ways: - It includes a \(D/r^8\) dipole-quadrupole correction term - The repulsion uses the form \(A \exp(-r/\rho)\) rather than \(A \exp(-Br)\)

These extra terms provide better reproduction of melt structure and dynamics for CAS systems.

When to use BJP¶

Pure CAS glass studies — Ca-Al-Si-O compositions exclusively
Structural properties — well-validated for RDFs, coordination, and Qⁿ distributions in CAS melts
High-temperature melt dynamics — parameterized against ab initio MD of CAS melts

Limitations¶

Only 4 elements — cannot model glasses with Na, K, Mg, B, or other modifiers
Adding additional elements requires reparameterization
Not suitable for borosilicate or alkali silicate glasses