Hi, I am running a simulation which contains only water (using the spc216.gro coordinates and TIP3P model) in an NPT ensemble. I get different values for the average pressure in the x y and z directions. I am running the simulation for up to 10s in a 4nm side cube unit cell. I am using a Nose Hoover thermostat and a Parrinello-Rahman barostat applied isotropically, with target pressure 1 bar.
The averages after 1ns are: Energy Average Err.Est. RMSD Tot-Drift ------------------------------------------------------------------------------- Temperature 299.999 0.00098 6.07906 0.00504098 (K) Pressure 1.3174 0.066 350.061 -0.14372 (bar) Box-X 4.0396 0.00013 0.00874048 -5.7234e-06 (nm) Box-Y 4.0396 0.00013 0.00874048 -5.7234e-06 (nm) Box-Z 4.0396 0.00013 0.00874048 -5.7234e-06 (nm) Pres-XX 1.11668 2 485.28 0.288761 (bar) Pres-YY -0.762405 1 427.866 -6.2632 (bar) Pres-ZZ 3.59792 2.4 410.546 5.54328 (bar) The averages over the 10 ns are : Energy Average Err.Est. RMSD Tot-Drift ------------------------------------------------------------------------------- Temperature 300 8e-05 4.00951 0.000535848 (K) Pressure 1.22566 0.0067 275.993 -0.0289005 (bar) Box-X 4.03929 5.1e-05 0.00823878 0.000126042 (nm) Box-Y 4.03929 5.1e-05 0.00823878 0.000126042 (nm) Box-Z 4.03929 5.1e-05 0.00823878 0.000126042 (nm) Pres-XX 1.29387 0.73 385.989 0.0898956 (bar) Pres-YY 1.35691 0.74 378.841 3.13618 (bar) Pres-ZZ 1.02621 0.84 377.022 -3.31278 (bar) Why is the average pressure in the in each direction different? And why is the drift of the XX direction so much lower than in the YY and ZZ directions? Many thanks! -- Gromacs Users mailing list * Please search the archive at http://www.gromacs.org/Support/Mailing_Lists/GMX-Users_List before posting! * Can't post? Read http://www.gromacs.org/Support/Mailing_Lists * For (un)subscribe requests visit https://maillist.sys.kth.se/mailman/listinfo/gromacs.org_gmx-users or send a mail to gmx-users-requ...@gromacs.org.
