Dear Gromacs,

I have been calculating the self Diffusion constant of my system. Surfactants in a different solvents of the same volume. After simulation for 20ns I found the following data for the trajectory of the mean square displacement.

# D[       TPA] = 0.2039 (+/- 0.0503) (1e-5 cm^2/s)
         0           0
         2   0.0105286
         4   0.0162435
         6   0.0212711
         8    0.026031
        10   0.0307584
        12    0.035134
        14   0.0393323
        16   0.0434628
        18   0.0475354
        20   0.0516609
         -
         -
         -
         -
         -
         -
       920     1.16467
       922     1.16756
       924      1.1703
       926     1.17267
       928     1.17383
       930     1.17483
       932     1.17581
       934     1.17754
       936     1.17957
       938     1.18199
       940      1.1829
       942     1.18596
       944     1.18871
       946     1.19099
       948     1.19219
       950     1.19321
       952     1.19445
       954     1.19613
       956     1.19838

         -
         -
         -
         -
         -
         -
     10576     11.7747
     10578      11.785
     10580     11.7817
     10582     11.7833
     10584     11.7847
     10586      11.784
     10588     11.7855
     10590     11.7904
     10592     11.7926
     10594     11.7943
     10596     11.8036
     10598     11.8141
     10600     11.8112

         -
         -
         -
         -
         -
         -
     19960     36.4106
     19962     36.2607
     19964     39.9243
     19966     39.7493
     19968     39.6744
     19970     39.5838
     19972     39.6723
     19974     39.6374
     19976      39.518
     19978     39.4935
     19980     39.3834
     19982     39.1136
     19984     42.3888
     19986      42.168
     19988     42.1337
     19990     41.9395
     19992     42.0065
     19994     42.0993
     19996     41.8652
     19998     41.8419
     20000     41.9419
     20002     41.6049


From my data, the graph shows a linear trend until 18ns but as soon as it reaches around 19, 20ns it dramatically increases the MSD value. Since the surfactants form aggregation I was expecting the MSD curve to go down. Is any explanation for that. Why? suddenly increases the MSD curve. Which is then the correct slop then!


Thank you

Rob


Quoting "Justin A. Lemkul" <jalem...@vt.edu>:



Paymon Pirzadeh wrote:
I assumption was that when provide the index file, do_dssp will do the
analysis for the protein but prints out the results only for the
designated residues. All I wanted was a better resolution on the final

When prompted for only one group, that group is used for calculation and output.

xpm plot to see the secondary structure of the protein at those residues
of interest. Any suggestions on how we can increase the resolution of
dssp plot and enlarging the axis of residues?

Yes, use an .m2p file to adjust the matrix spacing. This was discussed several days ago.

By the way, what would the option -nice do here?


Likely nothing.  Nice levels are irrelevant for most tasks.

-Justin

Paymon On Wed, 2010-10-06 at 15:29 -0400, Justin A. Lemkul wrote:
Paymon Pirzadeh wrote:
Justin,
I produced the index file based on your suggestion, but when I ran the
do_dssp, a completely different result was spit out comparing to what
the whole protein analysis had given. Any ideas on why that might have
happened?

That depends on what "completely different" means. I have no idea. If you're only analyzing a subset of the residues, you're going to get a discontinuous plot that's probably going to look a whole lot different from any analysis done on the whole protein. What's more, if you're only considering small fragments of the protein, then omitting surrounding residues from the analysis probably won't permit DSSP to find hydrogen bonding partners that are necessary to determine the correct secondary structure.

-Justin

Paymon

On Wed, 2010-10-06 at 14:42 -0400, Justin A. Lemkul wrote:
Paymon Pirzadeh wrote:
Hello, I want to check the secondary structure of protein at particular
residues. Since dssp needs all main chain atoms, does the following command
at the make_ndx prompt makes the correct index file?
You can answer that yourself by looking at the resulting index file.

5 | r 1 | r 10-11 |r 14-17 | r 20-21 | r 26-32 | r 42 | r 45

To get these groups to merge, I think you probably need to do 5 & r 1 | ...

-Justin

(Main chain atom of particular residues). regards,

Paymon

--
========================================

Justin A. Lemkul
Ph.D. Candidate
ICTAS Doctoral Scholar
MILES-IGERT Trainee
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080
http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin

========================================

--
========================================

Justin A. Lemkul
Ph.D. Candidate
ICTAS Doctoral Scholar
MILES-IGERT Trainee
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080
http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin

========================================



--
========================================

Justin A. Lemkul
Ph.D. Candidate
ICTAS Doctoral Scholar
MILES-IGERT Trainee
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080
http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin

========================================
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