<div class="gmail_quote">On Wed, May 27, 2009 at 1:36 PM, Jussi Lehtola <span dir="ltr"><<a href="mailto:jussi.lehtola@helsinki.fi">jussi.lehtola@helsinki.fi</a>></span> wrote:<br><div> </div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
In the twin range method [1] interactions that are in the range<br>
rlist..rvdw are only calculated during neighborlist updates. In the mean<br>
time they are considered to stay constant.<br>
<br>
The idea behind this is that when r>rlist the interactions are weaker<br>
and also vary more slowly, thus one doesn't need to be as precise in<br>
taking those interactions into account.<br>
<br>
[1] <a href="http://dx.doi.org/10.1002/prot.340060203" target="_blank">http://dx.doi.org/10.1002/prot.340060203</a></blockquote><div><br><br>Thanks for your explanation and the link for the reference.<br><br>I think you are right. The interactions between pairs within the range
rlist..rvdw are computed and stored when neighborlists are updated, and added as constant to short-range forces within rlist at every step between successive neighborlist updates.<br><br>It seems that in the twin range cut-off method, rlist does not only
play a role as a cut-off for neighbor searching, but also as a cut-off
for short-range interactions. Do I understand correctly?<br><br>I also agree with you that interactions are weak when r>rlist. So it seems reasonable to use this twin range cut-off algorithm.<br><br>However, if we compare the original Verlet list algorithm and the twin range cut-off algorithm, I think there is a shorting coming of the twin range cut-off algorithm to consider the particles which diffuse and across the boundary of rlist between successive neighborlist updates. The particles which move into the radius of rlist will not be calculated between successive neighborlist updates. On the other hand, some particles can move out of the radius of rlist between successive neighborlist updates. If rlist is really a cut-off for short range interaction, such out moving particle will not bring too much trouble for the calculation of forces. However, if rlist is only a cut-off for neighbor searching but not for short range interactions, such out moving particles will give a particle-based cut-off for short range interaction rather than a well-defined distance-based cut-off for forces. <br>
<br>Do people think the effect of these inward moving and outward moving particles is small and the error for calculation can be tolerated?<br></div></div><br>Thanks!<br><br>Yan<br><br>