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<div class="moz-cite-prefix">Dear David,<br>
an AQCC (or MRCI) wave function is a sum of Slater derminants,
each of them specified by orbital occupancies. <br>
Natural orbital occupancies less than 2 indicate than in some of
the derminants those orbitals are not <br>
doubly occupied; in practice an exact 2 occupancy implies those
orbitals are not correlated, ie, they are `CORE' orbitals.
Orbitals which are CLOSED are not included in the active space but
*are* correlated at the CISD level, i.e. determinants with single
and double excitations out of those orbitals *are* included in the
AQCC expansion, hence their occupancies will be less than 2.<br>
Having virtual orbitals with non-zero occupancies is also normal
and indicates that some excited configuration in which the
orbitals in question are occupied has a relatively high weight in
the AQCC expansion.<br>
<br>
Lorenzo<br>
<br>
<br>
On 17/06/14 02:32, David Scarborough wrote:<br>
</div>
<blockquote
cite="mid:CAPOy8zePNWNqcrr9gqmCYh7Z+0pE+N8L9yL_ARLDO9EeFqiGag@mail.gmail.com"
type="cite">
<div dir="ltr">
<div>Hello,</div>
<div> </div>
<div>I'm running a MRAQCC single point energy calculation with
the following input:</div>
<div> </div>
<div>{mcscf,maxit=100<br>
occ,26<br>
closed,20<br>
wf,nelec=46,spin=0,charge=0,sym=1<br>
print,orbitals,virtuals<br>
cpmcscf,hess<br>
}</div>
<div> </div>
<div>{aqcc,maxit=250<br>
core,6<br>
wf,nelec=46,spin=0,charge=0,sym=1<br>
natorb,print=20<br>
}</div>
<div> </div>
<div>The natural orbitals from the AQCC step suggest that the
six core orbitals have double occupancy but the remaining 14
closed orbitals do not. Also the virtual orbitals from number
27 onwards have non-zero occupancies. Is there an error in my
input that is resulting in the closed orbitals not maintaining
an occupancy of two? Why are the virtual orbitals outside the
active space occupied?</div>
<div> </div>
<div>I obtain the same solution whether I include the occ and
closed commands in the AQCC block or not.</div>
<div> </div>
<div>Thank you for your help.</div>
<div>David.<br clear="all">
</div>
<div>Postgraduate research student</div>
<div><a moz-do-not-send="true"
href="mailto:david.l.scarborough@gmail.com">david.l.scarborough@gmail.com</a></div>
</div>
<br>
</blockquote>
<br>
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