[AMBER] Diffusion constant's unit

From: Vijay Manickam Achari <vjrajamany.yahoo.com>
Date: Wed, 7 Aug 2013 04:33:24 +0100 (BST)

Dear sir,
Greetings.

I need some clarification on determining the diffusion constant via ptraj.

It is stated in the diffusion output that:

DIFFUSION
� � � Only the average results will be dumped to diffusion-malto-thermo63.dat_?.xmgr
� � � The time between frames in psec is 5.000.
� � � To calculated diffusion constants, calculate the slope of the lines(s)
� � � and multiply by 10.0/6.0; this will give units of 1x10**-5 cm**2/s
� � � The atoms in the calculation follow: :63�

This meas if get the gradient value about 0.3 (for example), I should multiply this value (0.3) with 10/6 and I will get 0.5.�

This value now can be written as 0.5 x 10e-5 cm^2/s.

Is that we multiply with 10 here to get the units fromangstrom^2/ps to cm^2/s ?

Because when I convert angstrom^2/ps to cm^2/s �I get 10e-4 instead 10e-5 as given in the amber manual.

1 angstrom �= 10e-8 cm
so�1 angstrom^2 �= 10e-16 cm^2

1ps = 10e-12 s


so �1 angstrom / 1 ps �
= 10e-16/10e-12�
= 10e-4 cm^2/s

May I know how the 10e-5 cm^2/s as in the manual is obtained?

This�verification�may help a lot for me and others.

Many thanks in advance.
Regards


Vijay Manickam�
Chemistry Department,
University of Malaya,
Malaysia
vjramana.gmail.com
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Received on Tue Aug 06 2013 - 21:00:02 PDT
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