Dear experts,<br><br>I am intending to calculate the equilibrium density of a pure hydrocarbon at different pressures , at 425 K. The normal boiling point of the liquid is around 350 K. For pressures below 100 bar densities I am getting from NPT is in accurate. I start form a structure which is compressed to above 0.6 g/cm3 density but since temperature is high density goes than to the values below. <br>
<br>P = 50 bar > NPT rho= 0.344 experimental density ~ 0.54<br>P 100 > NPT rho= 0.43 experimental density ~ 0.55<br><br>densities become more accurate for P >100 bar. <br><br>P 500 > rho= 0.56 experimental density ~ 0.61<br>
<br>I thought maybe you have some idea on how this inaccuracy can be improved.<br><br>Thank you in advance for your invaluable help.<br>Best,<br><br><br>; Bonds<br>
constraints = none <br>
constraint-algorithm = lincs<br> <br>; Run control <br>integrator = md <br>dt = 0.001 <br>nsteps = 5000000 <br>nstcomm = 100 <br>
<br>; Output control<br>nstenergy = 100 <br>nstxout = 100 <br>nstvout = 0<br>nstfout = 0<br>nstlog = 1000 <br>
nstxtcout = 1000 <br><br>; Neighbor searching<br>nstlist = 10 <br>ns_type = grid <br><br>; Electrostatics/VdW <br>coulombtype = Shift <br>
vdw-type = Shift <br>rcoulomb-switch = 0 <br>rvdw-switch = 0.9 <br><br>; Cut-offs<br>rlist = 1.25 <br>rcoulomb = 1.0 <br>
rvdw = 1.0 <br><br>; Temperature coupling <br>Tcoupl = v-rescale <br>tc-grps = System <br>tau_t = 0.1 <br>
ref_t = 425 <br> <br>; Pressure coupling<br>Pcoupl = berendsen <br>Pcoupltype = isotropic <br>tau_p = 1 <br>
compressibility = 3.5e-5 <br>ref_p = 100 <br><br>; Velocity generation <br>gen_vel = no;yes <br>gen_temp = 425 <br>
gen_seed = 173529 <br><br><br><br><br>