Re: Characteristic time of atomic vibrations and collisions?

From: Victor Ovchinnikov (ovchinnv_at_MIT.EDU)
Date: Mon Jan 14 2008 - 17:33:42 CST

Long,
You need to consider bond stretching frequencies, which will be of the
order of 2000 cm-1; this corresponds roughly to 17 fs per period.
Victor

On Mon, 2008-01-14 at 17:16 -0500, Yinglong Miao wrote:
> Dear NAMD users,
>
> Here I have a quite fundamental question generally for MD. 1fs is the
> typical MD timestep we have been using for MD simulations. But as I
> searched for information about characteristic time of atomic vibrations
> and collisions, I found 10^12 for the atomic vibration frequency on one
> of the websites. This should indicate the characteristic time as
> 10^(-12) s, which is 10^3 times larger than our MD timestep. It's right
> that the MD timestep needs to be smaller than the fastest vibrational
> frequency in the system, but how can this gap be so big? Or the number
> I found is not correct in some sense?
>
> Thanks,
> Long
>
> --
> Yinglong Miao
> Ph.D. Candidate
> Center for Cell and Virus Theory
> Chemistry Department, Indiana University
> 800 E Kirkwood Ave Room C203A, Bloomington, IN 47405
> Tel: 1-812-856-0981
>

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