Hi,


On 06.03.2009, at 12:37, "Vitaly V. Chaban" <[email protected]> wrote:

Hi,

I checked the VACF calculation with the results obtained with my
utility, it's completely correct with
g_velacc_402f -acflen 1001 -nonormalize -n an.ndx -mol
where an.ndx contains all the number of atoms of the needed molecule.

sounds very good. In my opinion it is a question of units. After using g_analyze you end up with nm^2 / ps very uncommon for a diffusion coefficient. So if you convert this to more convenient units you should obtain the expected value.
Cheers
Flo
The problem is evidently in the integration. I suspect it's something
with units there.

Does
g_analyze -integrate
give a pure integral of the function supplied? '*1/3' is not performed
(at least there is nothing about it in the manual)...

Vitaly

Hi Flo,

Yes, I remember our talk about this problem about a year ago.

So what should be the correct notation now?

I just tried
g_velacc_402f -acflen 1001 -nonormalize -n an.ndx
or
g_velacc_402f -acflen 1001 -nonormalize -n an.ndx -mol
and then g_analyze -integrate -f vac.xvg

but they give me a value close to 0...

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