Get the target pressure in fix gcmc

Hi, lammps user,

I encountered some difficulties about the temperature and pressure control. Thanks to the helps from some users, I have get a steady state. I find that the MC moves in fix gcmc is defective when I use it to get a steady state. So, when I make the M equal to 0, not perform the MC move, the temperature and the pressure of my system come to steady! I have not use any other temperature control algorithm, and just make the parameter tfac_insert==1.
Ok, another problem raised. I want to get the state in which pressure is about 50MPa, and I set the pressure to 50MPa in fix gcmc, but I get the lower pressure ~ 44 MPa. I used the pressure and fugacity_coeff replacing the chemical potential, and the Peng-Robinson state equation to calculate the fugacity_coeff. I guess this problem is related to the fugacity_coeff. So, how can I get the pressure set in fix gcmc? Thank in advance!

Don B.