Revisiting the birth of NaCl crystals using molecular dynamics simulation

Area of Science:

• Physical Chemistry
• Materials Science
• Computational Chemistry

Background:

• Phase separation in oversaturated electrolytic solutions is crucial for understanding crystallization processes.
• Classical nucleation theory provides a framework for solid formation, but initial stages require detailed investigation.

Purpose of the Study:

• To investigate the initial phase separation mechanisms in oversaturated electrolytic solutions.
• To develop a computationally efficient method for identifying the onset of ionic cluster formation.
• To analyze how varying concentrations influence the phase separation pathway.

Main Methods:

• Utilized molecular dynamics simulations to model oversaturated electrolytic solutions.
• Developed a novel, low-cost methodology involving box discretization to pinpoint cluster nucleation.
• Analyzed cluster growth and calculated the Steinhardt parameter to assess solid symmetry.

Main Results:

• Identified distinct phase separation mechanisms at different concentrations: one-stage transition (intermediate) and two-stage transition (high).
• Observed no stable cluster formation at low concentrations.
• High concentrations showed initial dense liquid formation followed by crystalline solid precipitation.
• Steinhardt parameter calculations supported classical nucleation theory for solid formation.

Conclusions:

• The developed methodology effectively identifies phase separation mechanisms during nucleation.
• Concentration-dependent phase separation pathways highlight the importance of the driving force for separation.
• Understanding these mechanisms is key for controlling crystallization in electrolytic solutions.