cannot melt quartz using bks_lj potential

I am using pair_style table (bks potential + lj potetnial) for beta_quartz and want to melt it use NPT. But I tried different ways: gradually increase the temperature of the system, create a velocity of 8000 K and then do NPT. In both cases the sample cannot melt. Why would this happen?


Could be lots of reasons, melting/solidification can be tricky.