Dear all,<br><br>I noticed that applying Parrinello-Rahman (PR) pressure coupling even after equilibration with berendsen does not lead to target value for pressure when <br><br>; Bonds<br>constraints = none<br>
<br>is used. I tried Berendsen for to get fixed pressure ( 50 bar) but in the next run PR even for long time is giving 52 bar. This is the case for other target pressures too.<br><br>So this made me select Berenden which is giving target pressure values but my concern is whether my results are reliable because BR does not give the exact ensemble as PR. I read somewhere on the list that fluctuation properties can not be calculated when BR is used. What does "fluctuation property" mean?<br>
<br>Does this mean that any property calculated form fluctuations of some other quantity can not be obtained>? like heat capacity which is defined based on enthalpy fluctuations? <br><br>I am interested in potential energy terms (g_energy bonded/non boned terms) and structural properties like rdf for a number of polymer molecules, system size around 3000 atoms. <br>
<br>Thank you for your comments.<br>Best,<br><br>
constraints = none <br>
<br>; Run control <br>integrator = md <br>dt = 0.002 <br>nsteps = 5000000 <br>nstcomm = 100 <br>
<br><br>nstenergy = 100 <br>nstxout = 100 <br>nstlist = 10 <br>ns_type = grid <br><br>coulombtype = Shift <br>
vdw-type = Shift <br>rcoulomb-switch = 0 <br>rvdw-switch = 0.9 ;0 <br><br>; Cut-offs<br>rlist = 1.25 <br>rcoulomb = 1.0 <br>
rvdw = 1.0 <br><br>Tcoupl = v-rescale <br>tc-grps = System <br>tau_t = 0.1 <br>ref_t = 300 <br>
<br>Pcoupl = berendsen <br>Pcoupltype = isotropic <br>tau_p = 1 <br>compressibility = 3.5e-5 <br>ref_p = 10 <br>
<br> <br>gen_vel = no<br>gen_temp = 300.0 <br>gen_seed = 173529 <br><br><br><br><br><br>