<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Dear Dmitrii, <div class=""><br class=""></div><div class="">in principle you are obviously right. However, due to the fact that in a numerical calculation the </div><div class="">number of particles is finite and typically small, the sum of all forces is fluctuating. If everything </div><div class="">else is correct, the effect is expected to vanish with increasing system size. You can fix the center </div><div class="">of mass by setting COMVEL_TOL to 0, but in general this is should not be necessary and if so </div><div class="">likely points to a source of systematic bias in your calculations. </div><div class=""><br class=""></div><div class="">Greetings, </div><div class="">Thomas</div><div class=""><br class=""><div><blockquote type="cite" class=""><div class="">Am 08.04.2020 um 19:59 schrieb Dmitrii Nikolaev <<a href="mailto:dmitrii....@gmail.com" class="">dmitrii....@gmail.com</a>>:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class="">Dear collegues,<div class=""><br class=""></div><div class="">I am running the Born-Oppenheimer molecular dynamics, and I notice that the sum of the forces on all atoms of my molecule is non-zero. However, as I understand for the NVE ensemble the total force should be zero? What is the reason for this force? </div><div class=""><br class=""></div><div class="">Thank you in advance,</div><div class="">Dmitrii</div></div><div class=""><br class="webkit-block-placeholder"></div>
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