i wonder if it is any way to get the desired density,pressure by Lammps.

for example with copper at room T= 300 K the density is 8.96 g/cm3.

to adjust it

Weight = (Number of atoms)*( atomic weight) = 2048*63,546= 130 142 g/mol

Volume = (Lattice fcc*Region block)^3= (28,906)^3= 24 152 a^3

Weight/Volume=5,38 g/(mol.a^3)=8,95 g/Cm^3

The pairwise potential used is Lennard-Jones : Depth of the potential well : 39.52 Finite distance: 2.3377 Rcut: 6.99

Normally in NVT group if i adjust my system to get the appropriate density i lose the pressure which should be approximately 1 atm.