<HTML><BODY style="word-wrap: break-word; -khtml-nbsp-mode: space; -khtml-line-break: after-white-space; "><FONT class="Apple-style-span" face="Helvetica Neue">Dear all,</FONT><DIV><FONT class="Apple-style-span" face="Helvetica Neue"><BR class="khtml-block-placeholder"></FONT></DIV><DIV><FONT class="Apple-style-span" face="Helvetica Neue">I am trying to find out exactly how the DDR program works in molpro. In short, my questions are:</FONT></DIV><DIV>1. What is the reference <B><I>J. Chem. Phys. 102, 0000, (1999) </I></B><FONT class="Apple-style-span" face="Helvetica Neue"><B> </B></FONT>in section 20.5.8. </DIV><DIV>2. How does DDR calculate the unitary transformation matrix.</DIV><DIV>3. What is the first orbital correction correction to the orbitals mentioned in section 39? How is this calculated?</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>For more context see below.</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>Thanks,</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>Chris Evenhuis</DIV><DIV><FONT class="Apple-style-span" face="Helvetica Neue"></FONT><BR class="khtml-block-placeholder"><DIV><FONT class="Apple-style-span" face="Helvetica Neue"><BR class="khtml-block-placeholder"></FONT></DIV><DIV><FONT class="Apple-style-span" face="Helvetica Neue">Firstly, the CASSCF orbitals are rotated to maximise the overlap with the reference orbitals using the diabatisation from section 20.5.8. From section 20.5.8:</FONT></DIV><DIV><FONT class="Apple-style-span" face="Helvetica Neue"><BR class="khtml-block-placeholder"></FONT></DIV><DIV><FONT class="Apple-style-span" face="Helvetica Neue">"<FONT class="Apple-style-span" face="Helvetica"><I>Recently, an automatic procedure, as described in <B>J. Chem. Phys. 102, 0000, (1999)</B> has been implemented into MOLPRO. This is available in Version 99.1 and later and is described in section 35."</I></FONT></FONT></DIV><DIV><I><BR class="khtml-block-placeholder"></I></DIV><DIV><FONT class="Apple-style-span" face="Helvetica Neue">In section 35 there is a reference to <B>D. Simah, B. Hartke, and H.-J. Werner, J. Chem. Phys. 111, 4523 (1999)</B>. Is this the mystery reference from above? From the description I see that the CASSCF orbitals are diabatised by either 2x2 Jacobi rotations or block diagonalisation.</FONT></DIV><DIV><FONT class="Apple-style-span" face="Helvetica Neue"><BR class="khtml-block-placeholder"></FONT></DIV><DIV><FONT class="Apple-style-span" face="Helvetica Neue"><BR class="khtml-block-placeholder"></FONT></DIV><DIV><FONT class="Apple-style-span" face="Helvetica Neue">Having a minimised the change in the CASSCF orbitals (and hence maximising the change in CI coefficients) DDR is used to find the unitary transformation that minimises the change in the CI coefficients. How is this achieved?</FONT></DIV><DIV><FONT class="Apple-style-span" face="Helvetica Neue"><BR class="khtml-block-placeholder"></FONT></DIV><DIV><FONT class="Apple-style-span" face="Helvetica Neue">A.<SPAN class="Apple-tab-span" style="white-space:pre"> </SPAN> minimising</FONT></DIV><DIV><SPAN class="Apple-tab-span" style="white-space:pre"> </SPAN><FONT class="Apple-style-span" face="Helvetica Neue">|< \phi_i(q')| \phi_i(q) >|^2+|< \phi_j(q')| \phi_j(q) >|^2</FONT></DIV><DIV><FONT class="Apple-style-span" face="Helvetica Neue"><SPAN class="Apple-tab-span" style="white-space:pre"> </SPAN>for each pair of active orbitals.</FONT></DIV><DIV><FONT class="Apple-style-span" face="Helvetica Neue"><BR class="khtml-block-placeholder"></FONT></DIV><DIV><FONT class="Apple-style-span" face="Helvetica Neue">B. <SPAN class="Apple-tab-span" style="white-space:pre"> </SPAN>or from the overlap matrix S = <\phi_i(q)|\phi_j(q)> as</FONT></DIV><DIV><FONT class="Apple-style-span" face="Helvetica Neue"><SPAN class="Apple-tab-span" style="white-space:pre"> </SPAN> <FONT class="Apple-style-span" face="Monaco">S(S^\dag S)^{-1/2}</FONT></FONT></DIV><DIV><FONT class="Apple-style-span" face="Monaco"><BR class="khtml-block-placeholder"></FONT></DIV><DIV>C. <SPAN class="Apple-tab-span" style="white-space:pre"> </SPAN>or something else</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>The examples then mention a first order correction for the change in the orbitals. What is this and how is it calculated?</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV><BR class="khtml-block-placeholder"></DIV></DIV></BODY></HTML>