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.TH "NATURAL_ORBITALS" "1" "Mar 07, 2019" "2.0" "Quantum Package"
.SH NAME
natural_orbitals \-  | Quantum Package >
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.SH SUMMARY
.sp
To produce state\-average natural orbitals, run
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.sp
.nf
.ft C
qp_run save_natorb file.ezfio
.ft P
.fi
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.sp
The MOs will be replaced, so the two\-electron integrals and the wave
function are invalidated as well.
.SH EXTRACTING NATURAL ORBITALS
.sp
Once obtained the near FCI wave function, one can obtain many
Onquantities related to it. e of these quantities are the natural
Onorbitals which have the properties of diagonalizing the one\-body
Ondensity matrix:
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.sp
.ce
\erho_{ij} = \edelta_{ij}
.ce 0
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.sp
where the element of the one\-body density matrix \erho_{ij} is
define as:
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.ce
\erho_{ij} = \elangle \ePsi | \eleft( a^{\edagger}_{j,\ealpha} a_{i,\ealpha} + a^{\edagger}_{j,\ebeta} a_{i,\ebeta} \eright) |\ \ePsi\ \erangle
.ce 0
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.sp
These orbitals are in general known to be better than the usual HF
MOs as they are obtained from a correlated wave function. To use these
orbitals for future calculations, one has to replace the current MOs
by the natural orbitals. To do so, just run:
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.sp
.nf
.ft C
qp_run save_natorb file.ezfio
.ft P
.fi
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.SH HANDS ON
.sp
\fBIMPORTANT:\fP
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As the MOs are changed, for the sake of coherence of future
calculations, the save_natorb program \fIautomatically removes the
current wave function\fP stored in the \fI\%EZFIO\fP database and replaces
it by a single Slater determinant corresponding to a HF occupation
of the new spin orbitals. Also, all the keywords to read the one\-
and two\-electron integrals on the MO basis are set to \fBNone\fP in
order to be sure to avoid reading integrals incompatible with the
current set of MOs\&.
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.sp
\fBSEE ALSO:\fP
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The documentation of the \fBsave_natorb()\fP program.
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.SH AUTHOR
A. Scemama, E. Giner
.SH COPYRIGHT
2019, A. Scemama, E. Giner
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