<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Dear Molpro Users,<div>I have been running local MP2 and CCSD(T) calculations on water clusters with various correlation consistent basis sets (aug-cc-pVnZ and cc-pVnZ with n=2,3,4). I have been seeing what seems to be an unusual result in the selection of the orbital domains.</div><div><br></div><div>The orbital domains I would naively expect to get are as follows: for each water molecule 2 domains consisting of only basis functions from the O atom (lone pairs) and 2 domains each consisting of basis functions from the O atom and one of the Hs (OH bonds). For almost all choices of basis set and using the same default value of THRBP=0.98 this is in fact what I am getting. For example, here are the domains I get for the water trimer using the avqz basis and THRBP=0.98:</div><div><br></div><div><div> <font class="Apple-style-span" face="Courier">Orbital domains</font></div><div><font class="Apple-style-span" face="Courier"><br></font></div><div><font class="Apple-style-span" face="Courier"> Orb. Atom Charge Crit.</font></div><div><font class="Apple-style-span" face="Courier"> 4.1 3 O7 1.12 0.000</font></div><div><font class="Apple-style-span" face="Courier"> 8 H8 0.60 1.000</font></div><div><font class="Apple-style-span" face="Courier"> 5.1 3 O7 1.10 0.000</font></div><div><font class="Apple-style-span" face="Courier"> 9 H9 0.56 0.999</font></div><div><font class="Apple-style-span" face="Courier"> 6.1 3 O7 1.34 0.997</font></div><div><font class="Apple-style-span" face="Courier"> 7.1 3 O7 1.26 0.999</font></div><div><font class="Apple-style-span" face="Courier"> 8.1 2 O4 1.26 0.999</font></div><div><font class="Apple-style-span" face="Courier"> 9.1 2 O4 1.34 0.997</font></div><div><font class="Apple-style-span" face="Courier"> 10.1 2 O4 1.12 0.000</font></div><div><font class="Apple-style-span" face="Courier"> 6 H5 0.59 1.000</font></div><div><font class="Apple-style-span" face="Courier"> 11.1 2 O4 1.10 0.000</font></div><div><font class="Apple-style-span" face="Courier"> 7 H6 0.55 0.999</font></div><div><font class="Apple-style-span" face="Courier"> 12.1 1 O1 1.10 0.000</font></div><div><font class="Apple-style-span" face="Courier"> 5 H3 0.56 0.999</font></div><div><font class="Apple-style-span" face="Courier"> 13.1 1 O1 1.34 0.997</font></div><div><font class="Apple-style-span" face="Courier"> 14.1 1 O1 1.26 0.999</font></div><div><font class="Apple-style-span" face="Courier"> 15.1 1 O1 1.12 0.000</font></div><div><font class="Apple-style-span" face="Courier"> 4 H2 0.60 1.000</font></div><div><br></div></div><div><br></div><div>I get the same domains for the vdz, vtz, vqz, avdz, and avqz basis sets. The lone exception is the avtz basis where for the water trimer I get the domains:</div><div><br></div><div><div> <font class="Apple-style-span" face="Courier">Orbital domains</font></div><div><font class="Apple-style-span" face="Courier"><br></font></div><div><font class="Apple-style-span" face="Courier"> Orb. Atom Charge Crit.</font></div><div><font class="Apple-style-span" face="Courier"> 4.1 3 O7 1.26 </font><font class="Apple-style-span" face="Courier"> 0.000</font></div><div><font class="Apple-style-span" face="Courier"> 8 H8 0.53 1.000</font></div><div><font class="Apple-style-span" face="Courier"> 5.1 3 O7 1.54 0.998</font></div><div><font class="Apple-style-span" face="Courier"> 6.1 3 O7 1.28 0.989</font></div><div><font class="Apple-style-span" face="Courier"> 7.1 3 O7 1.30 0.999</font></div><div><font class="Apple-style-span" face="Courier"> 8.1 2 O4 1.30 0.999</font></div><div><font class="Apple-style-span" face="Courier"> 9.1 2 O4 1.53 0.997</font></div><div><font class="Apple-style-span" face="Courier"> 10.1 2 O4 1.26 0.000</font></div><div><font class="Apple-style-span" face="Courier"> 6 H5 0.53 1.000</font></div><div><font class="Apple-style-span" face="Courier"> 11.1 2 O4 1.28 0.988</font></div><div><font class="Apple-style-span" face="Courier"> 12.1 1 O1 1.28 0.989</font></div><div><font class="Apple-style-span" face="Courier"> 13.1 1 O1 1.53 0.998</font></div><div><font class="Apple-style-span" face="Courier"> 14.1 1 O1 1.30 0.999</font></div><div><font class="Apple-style-span" face="Courier"> 15.1 1 O1 1.26 0.000</font></div><div><font class="Apple-style-span" face="Courier"> 4 H2 0.53 1.000</font></div><div><br></div><div>Further, if the avtz basis is used on the O atom and only vtz is used for the hydrogens I get the "expected" domains. I can also get the "expected" domains with avtz by increasing THRBP to 0.99, or by using the option pipek,delete=2.</div><div><br></div><div>I see the same behavior in the water dimer, trimer, tetramer and hexamer.</div><div><br></div><div>I understand that it is important to increase THRBP as the basis set is increased, and that diffuse functions can cause problems in the localization procedure. Therefore, on its own I am not surprised that the default options and the avtz basis do not give the "expected" domains. It is a little surprising in light of the fact that the default options and the avqz basis set do. I was also surprised to see the same behavior for the several different clusters. Furthermore, when using the avtz basis the domains will change when looking at different configurations of the clusters. Again, this is perhaps not surprising on its own, but it has not been the case for any of the other basis sets I have tested.</div><div><br></div><div>Is it just a coincidence that the default options are not sufficient with the avtz basis here, or perhaps a coincidence that they are sufficient with the avqz basis in this case? Is this a symptom that I am making some other mistake, or is it "normal" behavior when using the local methods?</div><div><br></div><div>Any insight anyone can share would be greatly appreciated.</div><div><br></div><div>regards,</div><div>Ben Shepler</div></div></body></html>