qp2/man/natural_orbitals.1

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.TH "NATURAL_ORBITALS" "1" "Jun 15, 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
quantities related to it. One of these quantities are the natural
orbitals which have the property of diagonalizing the one\-body
density 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
defined 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 save_natorb program.
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.SH AUTHOR
A. Scemama, E. Giner
.SH COPYRIGHT
2019, A. Scemama, E. Giner
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