Mismatch between gmx energy and gmx analyze

User discussions
1

GROMACS version: 2023
GROMACS modification: Yes

I am computing the surface tension of a biphase system. When I run gmx energy I get:

$ gmx energy -f ener.edr -s system.tpr -o surf-tens.xvg -b 5000
                     :-) GROMACS - gmx energy, 2024-dev (-:

Executable:   /usr/local/gromacs/bin/gmx
Data prefix:  /usr/local/gromacs
Working dir:  /home/michele/python_for_md/PentanolOPLSAA/NVT-surftens
Command line:
  gmx energy -f ener.edr -s system.tpr -o surf-tens.xvg -b 5000

Opened ener.edr as single precision energy file

Select the terms you want from the following list by
selecting either (part of) the name or the number or a combination.
End your selection with an empty line or a zero.
-------------------------------------------------------------------
  1  Bond             2  Angle            3  Ryckaert-Bell.   4  LJ-14         
  5  Coulomb-14       6  LJ-(SR)          7  Disper.-corr.    8  Coulomb-(SR)  
  9  Coul.-recip.    10  Potential       11  Kinetic-En.     12  Total-Energy  
 13  Conserved-En.   14  Temperature     15  Pres.-DC        16  Pressure      
 17  Constr.-rmsd    18  Vir-XX          19  Vir-XY          20  Vir-XZ        
 21  Vir-YX          22  Vir-YY          23  Vir-YZ          24  Vir-ZX        
 25  Vir-ZY          26  Vir-ZZ          27  Pres-XX         28  Pres-XY       
 29  Pres-XZ         30  Pres-YX         31  Pres-YY         32  Pres-YZ       
 33  Pres-ZX         34  Pres-ZY         35  Pres-ZZ         36  #Surf*SurfTen 
 37  T-System        38  Lamb-System   

36


Back Off! I just backed up surf-tens.xvg to ./#surf-tens.xvg.4#
Last energy frame read 15000 time 30000.000         

Statistics over 12500001 steps [ 5000.0000 through 30000.0000 ps ], 1 data sets
All statistics are over 125001 points

Energy                      Average   Err.Est.       RMSD  Tot-Drift
-------------------------------------------------------------------------------
#Surf*SurfTen                119.55          8    3483.46   -40.5338  (bar nm)

GROMACS reminds you: "If You Don't Like Cool Quotes Check Your GMXRC File" (Your Sysadmin)

But if I run gmx analyze on the same file I get:

$ gmx analyze -av -f surf-tens.xvg 
                    :-) GROMACS - gmx analyze, 2024-dev (-:

Executable:   /usr/local/gromacs/bin/gmx
Data prefix:  /usr/local/gromacs
Working dir:  /home/michele/python_for_md/PentanolOPLSAA/NVT-surftens
Command line:
  gmx analyze -av -f surf-tens.xvg

Read 1 sets of 12501 points, dt = 2

                                      std. dev.    relative deviation of
                       standard       ---------   cumulants from those of
set      average       deviation      sqrt(n-1)   a Gaussian distribition
                                                      cum. 3   cum. 4
SS1   1.260886e+02   3.450936e+03   3.086611e+01       0.010   -0.012


Back Off! I just backed up average.xvg to ./#average.xvg.4#

GROMACS reminds you: "Torture numbers, and they'll confess to anything." (Greg Easterbrook)

I guess the missmatch is due to gmx analyze using only roughly 1/10 of the data, but why is it so?