<div dir="ltr">I'm toying with CCSD natural orbitals for butadiene as a starting point for higher level calculations. Full input included at the end.<div><br><div><div>{ccsd;</div><div>expec,type=norelax;</div><div>dm,2141.2;</div><div>natorb,record=2141.2,print=23,<u>core</u>=0;</div><div>}</div></div><div><br></div><div>I'm confused as to the function of "<u>core</u>". The manual (<a href="https://www.molpro.net/info/2015.1/doc/manual/node341.html#sec:natorb_mp2" target="_blank" style="font-size:12.8px">https://www.molpro.net/<wbr>info/2015.1/doc/manual/<wbr>node341.html#sec:natorb_mp2</a>) states that core=1 freezes the core orbitals when constructing the density matrix. </div><div><br></div><div>If I'm already using the frozen-core approximation in my CCSD calculation, which I am, why does setting core=1 change my NO occupancy results? The core orbitals should not be coupled to the rest of the orbitals at all in a non-relaxed density matrix, so it should not matter if the core orbitals are included or not in the density matrix.</div><div><br></div><div>Any insight appreciated,</div><div>Alan Chien</div><div><br></div><div><br></div><div><br></div><div><u>Input below</u></div><div><u><br></u></div><div><div>***,buta</div><div>geometry={</div><div> C     0.6009903066  -0.4020172170   0.0000000000</div><div> C     -0.6009903066   0.4020172170   0.0000000000</div><div> C     1.8329498097   0.1103686968   0.0000000000</div><div> C     -1.8329498097  -0.1103686968   0.0000000000</div><div> H     1.9876059086   1.1777308428   0.0000000000</div><div> H     -1.9876059086  -1.1777308428   0.0000000000</div><div> H     0.4702284110  -1.4752930006   0.0000000000</div><div> H     -0.4702284110   1.4752930006   0.0000000000</div><div> H     2.7040838288  -0.5215644347   0.0000000000</div><div> H     -2.7040838288   0.5215644347   0.0000000000</div><div>}</div><div>basis=roos(3s2p1d/2s1p) !anos-l-pvdz</div><div>{hf;</div><div>orbprint,5;</div><div>}</div><div>{ccsd;</div><div>expec,type=norelax;</div><div>dm,2141.2;</div><div>natorb,record=2141.2,print=23,core=0;</div><div>}</div><div>{put,molden,ccsd.molden;</div><div>orbital,record=2141.2,type=natural</div><div>}</div></div><div><br></div><div><br></div><div><br></div><div><br></div></div></div>