<HTML><BODY style="word-wrap: break-word; -khtml-nbsp-mode: space; -khtml-line-break: after-white-space; ">Hi Ramon,<DIV><DIV><BLOCKQUOTE type="cite"><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">On the other hand, how do you handle constraints? Adjusting</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">velocities so that they do not modify constraints is not difficult,</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">and does not require iteration. But it leads to drifts. One must</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">constraint positions, and doing so would require either dropping</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">reversibility or iterating. Perhaps there is a method in the bibligraphy</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">to apply constraints in a reversible way.</DIV></BLOCKQUOTE></DIV><DIV><FONT class="Apple-style-span" color="#0000DD"><BR class="khtml-block-placeholder"></FONT></DIV><DIV>Unfortunately, when we digged through papers a couple of years ago the only solution for velocity verlet + constraints + PR coupling was iterating. However, IIRC, you only need to update the position constraints in the first iteration since the relative velocity over the bond vanishes after that.</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>The non-conservativeness of anisotropic pressure scaling is interesting, but also problematic since one of the premier applications would be membranes, where you obviously want separate coupling in the XY plane and Z normal :-) </DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>Cheers,</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>Erik</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>PS: Great to see some progress and discussion about this - we're quite interested, it's just that we've been too busy with other stuff!</DIV><BR><DIV> <SPAN class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><DIV>-----------------------------------------------------------</DIV><DIV>Erik Lindahl <<A href="mailto:lindahl@sbc.su.se">lindahl@sbc.su.se</A>></DIV><DIV>Assistant Professor, Stockholm Bioinformatics Center</DIV><DIV>Stockholm University, SE 106 91 Stockholm</DIV><DIV>Phone: +46 8 5537 8564 Fax: +46 8 5537 8214</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV><BR class="khtml-block-placeholder"></DIV><BR class="Apple-interchange-newline"></SPAN> </DIV><BR></DIV></BODY></HTML>