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.TH "CIS" "1" "Jun 15, 2019" "2.0" "Quantum Package"
.SH NAME
cis \-  | Quantum Package >
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.INDENT 0.0
.INDENT 3.5
Configuration Interaction with Single excitations.
.sp
This program takes a reference Slater determinant of ROHF\-like
occupancy, and performs all single excitations on top of it.
Disregarding spatial symmetry, it computes the \fIn_states\fP lowest
eigenstates of that CI matrix. (see \fBdeterminants n_states\fP)
.sp
This program can be useful in many cases:
.INDENT 0.0
.IP 1. 3
Ground state calculation
.sp
To be sure to have the lowest SCF solution, perform an scf
(see the module_hartree_fock module), then a \fI\%cis\fP, save the
natural orbitals (see save_natorb) and re\-run an scf
optimization from this MO guess.
.IP 2. 3
Excited states calculations
.sp
The lowest excited states are much likely to be dominated by
single\-excitations. Therefore, running a \fI\%cis\fP will save the
\fIn_states\fP lowest states within the CIS space in the \fI\%EZFIO\fP
directory, which can afterwards be used as guess wave functions for
a further multi\-state FCI calculation if \fBdeterminants
read_wf\fP is set to \fBtrue\fP before running the fci executable.
.UNINDENT
.sp
If \fBdeterminants s2_eig\fP is set to \fBtrue\fP, the CIS
will only retain states having the expected \ewidehat{S^2} value (see
\fBdeterminants expected_s2\fP). Otherwise, the CIS will take
the lowest \fBdeterminants n_states\fP, whatever multiplicity
they are.
.sp
\fBNOTE:\fP
.INDENT 0.0
.INDENT 3.5
To discard some orbitals, use the qp_set_mo_class
command to specify:
.INDENT 0.0
.IP \(bu 2
\fIcore\fP orbitals which will be always doubly occupied
.IP \(bu 2
\fIact\fP orbitals where an electron can be either excited from or to
.IP \(bu 2
\fIdel\fP orbitals which will be never occupied
.UNINDENT
.UNINDENT
.UNINDENT
.sp
Needs:
.INDENT 0.0
.INDENT 2.0
.IP \(bu 2
\fBread_wf\fP
.UNINDENT
.INDENT 2.0
.UNINDENT
.INDENT 2.0
.UNINDENT
.UNINDENT
.sp
Calls:
.INDENT 0.0
.INDENT 2.0
.IP \(bu 2
\fBrun()\fP
.UNINDENT
.INDENT 2.0
.UNINDENT
.INDENT 2.0
.UNINDENT
.UNINDENT
.sp
Touches:
.INDENT 0.0
.INDENT 2.0
.IP \(bu 2
\fBfock_matrix_ao_alpha\fP
.IP \(bu 2
\fBfock_matrix_ao_alpha\fP
.UNINDENT
.INDENT 2.0
.IP \(bu 2
\fBmo_coef\fP
.IP \(bu 2
\fBlevel_shift\fP
.UNINDENT
.INDENT 2.0
.IP \(bu 2
\fBmo_coef\fP
.IP \(bu 2
\fBread_wf\fP
.UNINDENT
.UNINDENT
.UNINDENT
.UNINDENT
.SH AUTHOR
A. Scemama, E. Giner
.SH COPYRIGHT
2019, A. Scemama, E. Giner
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