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68 lines
2.7 KiB
Groff
68 lines
2.7 KiB
Groff
.\" Man page generated from reStructuredText.
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.TH "CISD" "1" "Jan 16, 2019" "2.0" "Quantum Package"
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.SH NAME
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cisd \- | Quantum Package >
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.nr rst2man-indent-level 0
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..
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.de1 INDENT
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.\" .rstReportMargin pre:
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.de UNINDENT
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..
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.sp
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Configuration Interaction with Single and Double excitations.
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.INDENT 0.0
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.INDENT 3.5
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This program takes a reference Slater determinant of ROHF\-like occupancy,
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.sp
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and performs all single and double excitations on top of it, disregarding spatial symmetry and compute the “n_states” lowest eigenstates of that CI matrix (see \fBdeterminants n_states\fP).
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.sp
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This program can be useful in many cases:
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.INDENT 0.0
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.IP \(bu 2
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GROUND STATE CALCULATION: if even after a \fBcis()\fP calculation, natural orbitals (see \fBsave_natorb()\fP) and then \fBscf()\fP optimization, you are not sure to have the lowest scf solution, do the same strategy with the \fBcisd()\fP executable instead of the \fBcis()\fP\ exectuable to generate the natural orbitals as a guess for the \fBscf()\fP\&.
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.IP \(bu 2
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EXCITED STATES CALCULATIONS: the lowest excited states are much likely to be dominanted by single\- or double\-excitations. Therefore, running a \fBcisd()\fP will save the “n_states” lowest states within the CISD space in the EZFIO folder, which can afterward be used as guess wave functions for a further multi\-state fci calculation if you specify “read_wf” = True before running the fci executable (see \fBdeterminants read_wf\fP). Also, if you specify “s2_eig” = True, the cisd will only retain states having the good value S^2 value (see \fBdeterminants expected_s2\fP and \fBdeterminants s2_eig\fP). If “s2_eig” = False, it will take the lowest n_states, whatever multiplicity they are.
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.UNINDENT
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.sp
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Note: if you would like to discard some orbitals, use qp_set_mo_class to specify:
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.INDENT 0.0
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.IP \(bu 2
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“core” orbitals which will be always doubly occupied
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.IP \(bu 2
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“act” orbitals where an electron can be either excited from or to
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.IP \(bu 2
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“del” orbitals which will be never occupied
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.UNINDENT
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.UNINDENT
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.UNINDENT
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.sp
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File: \fBcisd/cisd.irp.f\fP
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.SH AUTHOR
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A. Scemama, E. Giner
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.SH COPYRIGHT
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2018, A. Scemama, E. Giner
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.\" Generated by docutils manpage writer.
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