Structural transitions of calcium carbonate by molecular dynamics simulation

Area of Science:

• Geochemistry
• Materials Science
• Computational Chemistry

Background:

• Calcium carbonate (CaCO3) is vital to the global carbon cycle.
• Understanding CaCO3 phase diagrams is critical for scientific research.
• Previous studies have explored various CaCO3 structures and transitions.

Purpose of the Study:

• To investigate selected structural phase transitions of calcium carbonate (CaCO3).
• To explore CaCO3 behavior under varying temperature and pressure conditions.
• To characterize phase transitions using molecular dynamics simulations.

Main Methods:

• Employed molecular dynamics simulations with the Raiteri potential.
• Simulations were conducted at constant pressure (1 bar) across temperatures (300-2500 K).
• Simulations were also performed at constant temperature (1600 K) across pressures (0-13 GPa).

Main Results:

• Temperature-driven transitions observed: calcite → CaCO3-IV → CaCO3-V, with increasing carbonate ion disorder.
• A continuous phase transition from CaCO3-IV to CaCO3-V was identified via free energy analysis.
• Pressure-driven transitions observed: CaCO3-V → CaCO3-IV at 2 GPa and CaCO3-IV → CaCO3-Vb at 4.25 GPa, the latter being first-order.

Conclusions:

• The study successfully characterized temperature- and pressure-induced phase transitions in calcium carbonate.
• Free energy analysis classified specific transitions as continuous or first-order.
• The findings provide valuable insights into the complex phase behavior of CaCO3 relevant to the carbon cycle.