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71 lines
2.4 KiB
Groff
71 lines
2.4 KiB
Groff
.\" Man page generated from reStructuredText.
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.TH "EXCITED_STATES" "1" "Jan 14, 2019" "2.0" "Quantum Package"
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.SH NAME
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excited_states \- | Quantum Package >
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.de1 INDENT
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.in \\n[rst2man-indent\\n[rst2man-indent-level]]u
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..
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.sp
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It is possible to run excited states calculations with the quantum package. To
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do this, set \fBdeterminants n_states\fP to the number of requested states.
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The selection criterion will be the maximum of the selection criteria for each
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state. If the Davidson diagonalization has difficulties to converge, increase
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the \fBdavidson n_states_diag\fP value.
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.sp
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When computing multiple states, it is good to have the \fBdeterminants
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s2_eig\fP flag \fBtrue\fP\&. This will force the Davidson algorithm to choose only
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vectors with a value of \ewidehat{S^2} equal to \fBdeterminants expected_s2\fP\&.
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Otherwise, different spin states will come out in the diagonalization.
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.sp
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The \fIQuantum Package\fP doesn’t take account of the symmetry. Due to numerical noise, excited
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states of different symmetries may enter in the calculation. Note that it is
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possible to make state\-average calculation of states with different symmetries
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and/or different spin multiplicities.
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.sp
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To include excited state of all possible symmetries, a simple trick is to
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run a preliminary multi\-state CIS calculation using the CIS program,
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and then running the selected FCI restarting from the CIS states, setting
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\fBdeterminants read_wf\fP to \fBtrue\fP\&.
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.sp
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Usually, it is good practice to use state\-averaged natural MOs so that all
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states have MOs of comparable quality. This allows for a faster convergence
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of excitation energies.
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.sp
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\fBSEE ALSO:\fP
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.INDENT 0.0
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.INDENT 3.5
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The documentation of the \fBscf()\fP, \fBcis()\fP and \fBfci()\fP programs.
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.UNINDENT
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.UNINDENT
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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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