The
structures of a single polyethylene chain were investigated
using all-atom molecular dynamics simulations with a series of cutoff
distances. We found that a long single chain with a short cutoff distance
undergoes coil, globule, and crystal states during a continuous cooling
process. The globule state vanishes for short chains less than a certain
length where there is large conformational fluctuation. A tight-folding
model was applied to analyze the folded structures, and the re-entry
modes show that a shorter chain prefers the nearest folding while
a longer one prefers the second or third nearest folding. Our results
show that a single polyethylene chain can exhibit condensed phenomena
of state transitions, which could be heuristic for single-chain physics
and polymer crystallization.