Qi-Jun Hong

Research

Small-cell Coexistence Method

An automated code is available at this site. (SLUSCHI, with interface to VASP)

Ta_16_duplicates_small_fast
  • System size is small (around 100 atoms).
  • Start from half-and-half solid-liquid coexistence.
  • Coexistence is not stable. It ends in a single phase.
  • MD trajectory is short.
  • Run multiple MD (NPT) duplicates to evaluate the probability distribution of the solid and the liquid Nliquid/Nsolid.
  • Infer the melting temperature based on the probability.

This movie (~1MB) shows the evolution of 16 duplicated cells with 108 Ta atoms at 3100 K. In terms of atomic configurations, solids display periodic patterns, while liquids do not. Liquids also have higher energy/enthalpies than solids. MDs start from half-and-half coexistence. All duplicates end in pure phases (either a solid or a liquid) in 6 picoseconds.

fit

Run NPT MDs at several temperatures and fit a melting point according to the following relations.

equations

Widom’s Particle Insertion Method

holes

Chemical potential can be calculated as the free energy difference upon inserting a test particle.

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