<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><br><div><div>On 2 Oct 2008, at 14:30, Lorenzo Lodi wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><span class="Apple-style-span" style="border-collapse: separate; 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; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0; ">To estimate the RAM requirement of a FCI calculation with molpro is it<span class="Apple-converted-space"> </span><br>preferable to use the Weil formula (which refers to the number of<span class="Apple-converted-space"> </span><br>spin-adapted configurations) or just binomial(2k,n), because Slater<span class="Apple-converted-space"> </span><br>determinants are used? And how does symmetry reduce the memory requirements?</span></blockquote><br></div><div>Neither. The code uses all Slater determinants of a particular M_S and a particular point group irreducible representation. Thus without symmetry the number is binom(m,N/2+M_S) * binom(m,N/2-M_S) for N electrons in m orbitals . With symmetry there is no simple exact formula, but just divide the no-symmetry number by the order of the group.</div><div><br></div><div>Peter</div><br><div apple-content-edited="true"> <span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13px; 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; "><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; "><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; "><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 style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; ">--</span></div><div style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; ">Prof. Peter J. Knowles </span></div><div style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; ">School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, UK</span></div><div style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; ">Telephone: +44 29208 79182 Fax: +44 2920874030 Email <a href="mailto:KnowlesPJ@Cardiff.ac.uk">KnowlesPJ@Cardiff.ac.uk</a> </span></div><div style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; ">WWW <span class="Apple-style-span" style="font-size: 13px; "><a href="http://www.cardiff.ac.uk/chemy/contactsandpeople/academicstaff/knowles.html">http://www.cardiff.ac.uk/chemy/contactsandpeople/academicstaff/knowles.html</a></span></span></div><br class="Apple-interchange-newline"></span></span></span></span></div></span> </div><br></body></html>