Re: Switch function equation

From: Brian Radak (bradak_at_anl.gov)
Date: Mon Oct 03 2016 - 21:16:58 CDT

This is (somewhat regrettably) implemented in multiple places in the
code - often piecewise. The function is:

S(r) = (r2^2 - r^2)^2 * (r2^2 - 3*r1^2 + 2*r^2) / (r2^2 - r1^2)^3

on the interval (r1, r2) where r1 = switchdist and r2 = cutoff (the
latter are the NAMD keyword names).

This is a sixth order polynomial, but I believe it is something like a
third order Chebyshev polynomial expansion of tan(2*x-1) when x is taken
as (r^2 - r1^2) / (r2^2 - r1^2) (or something similar)

HTH,

Brian

On 10/02/2016 11:57 PM, Faramarz Joodaki wrote:
> Hi everyone!
>
> I would be so grateful if you could tell me what is the exact switch function formula for non-bonded interaction in NAMD?
>
> Thank you!
> Faramarz
>
> Best Regards,
> Faramarz
>

-- 
Brian Radak
Postdoctoral Appointee
Leadership Computing Facility
Argonne National Laboratory
9700 South Cass Avenue, Bldg. 240
Argonne, IL 60439-4854
(630) 252-8643
brian.radak_at_anl.gov

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