[gmx-users] still change after equilibriated

[Rongliang Wu]

Hello gmx-users,

i have equilibriated a system after 7 ns, and out of curiosity i continued run until 9ns. but i found the following phenomenon:
          Statistics over 1000001 steps [ 5000.0000 thru 7000.0005 ps ], 9 data sets

Energy                      Average       RMSD     Fluct.      Drift  Tot-Drift
-------------------------------------------------------------------------------
Potential                  -8174.09          0          0 -0.0167593   -33.5187
Temperature                 299.735          0          0 -2.3866e-06 -0.0047732
Pressure (bar)             0.993253    417.974    417.974 -0.000471878  -0.943758
Box-X                       3.27009          0          0 -7.43729e-07 -0.00148746
Density (SI)                967.094          0          0 0.000662033    1.32407
Pres-XX (bar)               3.73019    721.395    719.606 -0.0879504   -175.901
Pres-YY (bar)               2.69262    624.848    623.924 -0.0588169   -117.634
Pres-ZZ (bar)              -3.44305    728.557    723.708   0.145352    290.704
#Surf*SurfTen              -21.9101    2811.25    2780.78   0.714987    1429.98
Heat Capacity Cv:      12.4718 J/mol K (factor = 0)

Statistics over 1000001 steps [ 7000.0005 thru 9000.0000 ps ], 9 data sets

Energy                      Average       RMSD     Fluct.      Drift  Tot-Drift
-------------------------------------------------------------------------------
Potential                  -8229.97          0          0  0.0348891    69.7783
Temperature                 299.735          0          0 1.12632e-06 0.00225264
Pressure (bar)              1.10322    419.616    419.616 -0.000406983  -0.813967
Box-X                       3.26972          0          0          0          0
Density (SI)                967.428          0          0 2.26927e-05  0.0453855
Pres-XX (bar)              -57.2399    737.021     736.43  0.0511137    102.227
Pres-YY (bar)                16.767    613.566    613.507 -0.0148347   -29.6693
Pres-ZZ (bar)               43.7826    732.279    731.959    -0.0375        -75
#Surf*SurfTen               209.332    2795.88    2793.91  -0.181749   -363.498
Heat Capacity Cv:      12.4718 J/mol K (factor = 0)
	
why the pressure in different orientations becomes much larger. is it that the only meaningful pressure value is the the scalar pressure?


Thanks!

Regards!
                    
Sincerely,

Rongliang Wu
State Key Laboratory
of Polymer Physics and Chemistry
Center of Molecular Science
Institute of Chemistry
Chinese Academy of Sciences
 				

　　　　　　　　　　wurl04 at iccas.ac.cn
　　　　　　　　　　2005-12-20