# Re: About the module of "External Electric Field "

From: Peter Freddolino (petefred_at_ks.uiuc.edu)
Date: Wed Jul 12 2006 - 02:02:03 CDT

Hi Wang,
just to be clear, the manual is referring to a temporal square wave, not
a spatial square wave. So, for example, the sequence of commands

eField 0 0 0
run 100
eField 0 0 10
run 100
eField 0 0 0
run 100

Produces a 300 step run with 100 steps of no field, 100 steps of a field
in the z direction, and 100 steps of no field again. Spatially
inhomogeneous fields cannot be simulated using this feature, and must
instead be treated using other means (such as tclForces).

Peter

wang wrote:
> Dear all ,
> Could you tell me how to assign a square wave to the value " *eField *" ?
> THX
> Wang
>
>
> External Electric Field
>
> NAMD provides the ability to apply a constant electric field to the
> molecular system being simulated. Energy due to the external field
> will be reported in the MISC column and may be discontinuous in
> simulations using periodic boundary conditions if, for example, a
> charged hydrogen group moves outside of the central cell. There are
> two parameters that control this feature.
>
> * *eFieldOn * $<$ apply electric field? $>$
> *Acceptable Values: * yes or no
> *Default Value: * no
> *Description: * Specifies whether or not an electric field is
> applied.
> * *eField * $<$ electric field vector $>$
> *Acceptable Values: * vector of decimals (x y z)
> *Description: * Vector which describes the electric field to be
> applied. Units are ${\rm kcal} / ({\rm mol \; \AA} \; e)$, which
> is natural for simulations. This parameter may be changed
> between run commands, allowing a square wave or other
> approximate wave form to be applied.
>
>

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