Re: LJ correction in NAMD2.7b3

From: Jim Phillips (
Date: Thu Aug 12 2010 - 15:14:41 CDT

The dynamics is only altered if pressure control is enabled, due to the
correction to the virial (and thus pressure) calculation. Because the
correction emulates the effect of the long-range 1/r^6 tails the
equilibrium cell volume will be slightly smaller. The forces calculated
for individual atoms are identical.


On Thu, 12 Aug 2010, Thomas C. Bishop wrote:

> Dear NAMD 2.7b3,
> I see you now have a LJCorrection option.
> As stated in the documentation (see below)
> this corrects only the _reported_ vdw energy.
> Does this option alter the dynamics in any way?
> Thanks
> Tom
> LJcorrection Apply long-range corrections to the system energy and virial to
> account for neglected vdW forces?
> Acceptable Values: yes or no
> Default Value: no
> Description: Apply an analytical correction to the reported vdW energy and
> virial that is equal to the amount lost due to switching and cutoff of the LJ
> potential. The correction will use the average of vdW parameters for all
> particles in the system and assume a constant, homogeneous distribution of
> particles beyond the switching distance. See [40] for details (the equations
> used in the NAMD implementation are slightly different due to the use of a
> different switching function). Periodic boundary conditions are required to
> make use of tail corrections. LJcorrection as implemented is inconsistent with
> vdwForceSwitching.
> *******************************
> Thomas C. Bishop
> Tel: 504-862-3370
> Fax: 504-862-8392
> ********************************

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