[gmx-users] g_velacc

[Ishwor]

Dear all 
I  have calculated the diffusion coefficient using command g_msd and I want
to calculate diffusion coefficient using command g_velacc. I am confused
with some terms. 
1>I have looked the manual page of g_velacc and i found the statement "the
time interval between data collection points is much shorter than the time
scale of the autocorrelation." What actually does that mean? 
2>I am also confused with the flag -acflen ( I have found that it describes
the number of frames to be taken into consideration.Does that mean I have to
take the points ,to integrate,  in such a way that it matches with the time
i have used in g_msd for fitting of Einsteins equation) 
3> what does the flag -nonormalize indicates. Do I need to use it
necessarily? 
4>Is the  command "g_analyze -f *.xvg -integrate" sufficient for
integration? 
Ishwor 
Nepal



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