[gmx-users] Lipid area calculation

[Yuhua Song]

Hi, Gromacs developer and users:

After I  equilibrate a 64 DPPC bilayer (download from peter's website), I intend to calculate the lipid area for
validation, the experimental value of a DPPC bilayer should be around 0.61nm^2 

My way to calculate the lipid area is:
1) to make index file for one DPPC 
2) use g_sas to calculate one DPPC area. The results shows as below, it seems that
it has nothing to do with 0.61nm^2 standard value.

I do not know what is wrong. My way to calculate the lipid area is wrong? could you
please help me out?

Thank you very much. Yuhua


# This file was created by /home/soft/cluster/gromacs/i686-pc-linux-gnu/bin/g_sas
# which is part of G R O M A C S:
# Good gRace! Old Maple Actually Chews Slate
# All this happened at: Sun Nov  9 21:37:12 2003
#
@    title "Solvent Accessible Surface"
@    xaxis  label "Time (ps)"
@    yaxis  label "Area (nm\S2\N)"
@TYPE xy
@ view 0.15, 0.15, 0.75, 0.85
@ legend on
@ legend box on
@ legend loctype view
@ legend 0.78, 0.8
@ legend length 2
@ s0 legend "Hydrophobic"
@ s1 legend "Hydrophilic"
@ s2 legend "Total"
@ s3 legend "D Gsolv"
         0     19.2265     9.33045      28.557           0
      0.05     19.0852     9.38099     28.4662           0
       0.1     19.2972     9.25305     28.5503           0
      0.15     19.2265     9.24634     28.4729           0
       0.2     19.3326     9.24634     28.5789           0
      0.25     19.3326     9.21771     28.5503           0
       0.3     19.4386     9.38315     28.8218           0
      0.35     19.4386     9.36124     28.7998           0
       0.4     19.2972     9.31702     28.6143           0
      0.45     19.2619     9.34565     28.6075           0
       0.5     19.2972     9.23114     28.5284           0
      0.55     19.1912     9.43825     28.6295           0
       0.6     19.2972     9.41178      28.709           0
      0.65     19.3679     9.29511      28.663           0
       0.7     19.3679     9.35908      28.727           0
      0.75     19.3326     9.31702     28.6496           0
       0.8     19.4033      9.2329     28.6362           0
      0.85     19.1559     9.21315      28.369           0
       0.9     19.3679     9.18236     28.5503           0
      0.95     19.2265     9.20428     28.4308           0
         1     19.2972     9.41633     28.7136           0
      1.05     19.3326     9.40114     28.7337           0
       1.1     19.0498     9.55315      28.603           0
      1.15     19.1559     9.31031     28.4662           0
       1.2     19.3679     9.28839     28.6563           0
      1.25     19.1205     9.21987     28.3404           0
       1.3     19.2265     9.21099     28.4375           0
      1.35     19.3679     9.28168     28.6496           0