[gmx-users] Fwd: Large pressure fluctuation

[Yutian Yang]

> Hi all, 
> 
> I have some problems with the pressure of my system. When I try to run equilibrium systems (NVT or NPT), I have got large pressure fluctuations (2 or 3 orders higher than average value). When I apply shear to the system, the pressure of the system increases with the increasing shear rate, which is normal, but the fluctuations don't change much. The following is the actual results for a (5nm)^3 box. Are these results normal? Or are there any problems with the simulations? 
> 
> Thank you so much! 
> 
> NVT:
> Energy                      Average   Err.Est.       RMSD  Tot-Drift
> -------------------------------------------------------------------------------
> Pressure                    71.1917        1.9    103.261   -3.68971  (bar)
> Pres-XX                     71.1268        1.7     150.31    -3.3972  (bar)
> Pres-XY                   -0.106214       0.37     94.633   0.382172  (bar)
> Pres-XZ                    0.182851       0.13    94.6965  0.0525603  (bar)
> Pres-YX                   -0.106214       0.37     94.633   0.382172  (bar)
> Pres-YY                     70.7725        2.1    150.345   -3.08484  (bar)
> Pres-YZ                    0.149167       0.42    94.5955    1.01412  (bar)
> Pres-ZX                    0.182851       0.13    94.6965    0.05256  (bar)
> Pres-ZY                    0.149166       0.42    94.5955    1.01412  (bar)
> Pres-ZZ                     71.6759        2.2    150.227   -4.58708  (bar)
> 
> NPT:
> Energy                      Average   Err.Est.       RMSD  Tot-Drift
> -------------------------------------------------------------------------------
> Pressure                   0.975026      0.042    89.3802  0.0580066  (bar)
> Pres-XX                     1.93729       0.43    139.974  -0.727682  (bar)
> Pres-XY                   -0.938744       0.65    93.4597    2.31599  (bar)
> Pres-XZ                  0.00540739       0.51    93.5049   -2.21079  (bar)
> Pres-YX                   -0.938744       0.65    93.4597    2.31599  (bar)
> Pres-YY                    -0.75967       0.61    140.338   0.703514  (bar)
> Pres-YZ                  -0.0475309       0.62    93.4529   0.234715  (bar)
> Pres-ZX                  0.00540704       0.51    93.5049   -2.21079  (bar)
> Pres-ZY                  -0.0475311       0.62    93.4529   0.234714  (bar)
> Pres-ZZ                     1.74746       0.47    140.156   0.198188  (bar)
> 
> Shear rate 0.04 1/ns
> Energy                      Average   Err.Est.       RMSD  Tot-Drift
> -------------------------------------------------------------------------------
> Pressure                    68.7197       0.83    103.185    3.16213  (bar)
> Pres-XX                     67.9871       0.96    150.379    4.90957  (bar)
> Pres-XY                    -1.87457       0.26     94.606    1.52909  (bar)
> Pres-XZ                    -0.14688       0.24    94.5825  -0.986185  (bar)
> Pres-YX                    -1.87457       0.26     94.606    1.52909  (bar)
> Pres-YY                     68.7435       0.94     150.28    1.77856  (bar)
> Pres-YZ                    0.406456       0.32    94.5859   -1.08897  (bar)
> Pres-ZX                    -0.14688       0.24    94.5825  -0.986184  (bar)
> Pres-ZY                    0.406456       0.32    94.5859   -1.08897  (bar)
> Pres-ZZ                     69.4285       0.73    150.176    2.79824  (bar)
> 
> Shear rate 52.3 1/ns
> Energy                      Average   Err.Est.       RMSD  Tot-Drift
> -------------------------------------------------------------------------------
> Pressure                    244.394        1.3    116.824   0.743594  (bar)
> Pres-XX                    -107.921        2.5    198.609   -6.31786  (bar)
> Pres-XY                    -386.103       0.32    101.948   -1.42629  (bar)
> Pres-XZ                  -0.0737284       0.46    100.128    2.03768  (bar)
> Pres-YX                    -386.103       0.32    101.948   -1.42629  (bar)
> Pres-YY                     459.455        1.1    154.569    3.95874  (bar)
> Pres-YZ                   -0.125439       0.17    95.0531    0.28234  (bar)
> Pres-ZX                  -0.0737286       0.46    100.128    2.03768  (bar)
> Pres-ZY                   -0.125439       0.17    95.0531    0.28234  (bar)
> Pres-ZZ                     381.649        1.2    152.955     4.5899  (bar)
> 
> Yutian
> 
>