I have created a Semi-crystalline (HDPE) structure using Amorphous and crystalline structures together in a layer (shown below). it has a density of 0.961g/cc. but while annealing this structure to approach final density, I drastically decreasing to density 0.74g/cc. 

Can anyone please help me to come out from this situation. i want final density to be 0.945g/cc

Thankyou 

Annealing temperature was set at 298K to 400K, but in starting the temperature showing 1100K which is extremely higher than melting point of HDPE (130C). i think has some thermal problem due to which I m get this much of variation in density. 

if i run it for 100-200ps, will it approach 0.945g/cc density?