Table 2.
Formation energies of magnesium substitution (substituting for calcium ions) into an energy optimized amorphous calcium phosphate model, based on a modified Posner’s Cluster.
| Structure | Particle Formula | Formation Energy (eV) |
|---|---|---|
| Unsubstituted primary cluster | Ca8(PO4)6H2 | – |
 |
Ca7Mg(PO4)6H2 | -0.463 |
| Ca6Mg2(PO4)6H2 | +1.644 | |
| Ca5Mg3(PO4)6H2 | +2.705 | |
| Mg-substituted clusters | Ca4Mg4(PO4)6H2 | +4.244 |
 |
Ca3Mg5(PO4)6H2 | +7.412 |
| Ca2Mg6(PO4)6H2 | +7.902 | |
| CaMg7(PO4)6H2 | +10.971 | |
| Lowest energy Mg-substituted HA | HA - Mg | +1.747 |
Substitution of a single Mg ion into a unit cell of hydroxyapatite (HA) is also presented. Positive formation energies indicate an unfavorable/unstable structure and negative formation energies a favorable/stable structure.