<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">Dear Somnath,<div class=""><br class=""></div><div class="">actually a reference function coefficient of 0.94 is ok and a contribution of about 35 mEh from the Davidson correction is not unusual. Remember that much of this will cancel in any energy difference, so it’s not like it will make a 1 eV change on any energetics of interest.</div><div class=""><br class=""></div><div class="">best regards,</div><div class=""><br class=""></div><div class="">-Kirk</div><div class=""><br class=""></div><div class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Sep 16, 2015, at 9:30 AM, Somnath BHOWMICK <<a href="mailto:somnath.bhowmick@etu.univ-amu.fr" class="">somnath.bhowmick@etu.univ-amu.fr</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="Content-Type" content="text/html; charset=utf-8" class=""><div class=""><div style="font-family: 'Times New Roman'; font-size: 18px;" class="">Dear Molpro users,<br class=""><br class="">I am calculating excited states of lithium and fluorine clusters in MRCI theory. The active space is large enough (around 85000 CSFs) to describe the ground and few low-lying excited states. There is a large gain in correlation energy (about 7-8 eV) from the reference energy at the MRCI level. Moreover, the coefficient of the reference function in the MRCI wave function, i.e. c_n (as mentioned in <a href="https://www.molpro.net/info/2012.1/doc/manual/node310.html" class="">https://www.molpro.net/info/2012.1/doc/manual/node310.html</a>) is only around 0.94. This makes a huge gain in correlation energy (1 eV) in the Davidson correction term (for both fixed and rotated references) from the conventional MRCI energy. I was wondering if this is normal for most MRCI calculations or there is a limit of this energy difference or there exist some predefined conditions on the breakdown of Davidson correction.<br class=""><br class="">Thank you in advance.<br class=""><br class=""><div style="font-family: 'Times New Roman'; font-size: 16px;" class=""><div style="text-align: left;" class=""><pre class="moz-signature" cols="72"><font size="3" class=""><span style="font-family: Georgia;" class="">With very best of regards<br class="">Somnath Bhowmick<br class=""><br class=""></span></font></pre></div>
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