Molecular Dynamics Study on Lubrication Mechanism in Crystalline Structure between Copper and Sulfur

Table 2

Calculation condition for structural optimization of Cu₂S crystal.

Exchange correlation potential	—	PBE-GGA
Energy to separate core from valence states	Ry	−6.0
Energy convergence criteria	Ry	0.0001
Change of ratio
Rate of change	%	+4+10
Increment of rate (for )	%	+2
Volume change
Rate of change	%	−2+6
Increment of rate (for )	%	+1

Energy unit: 1 Ry = J = 13.60 eV.