74 lines
2.4 KiB
Groff
74 lines
2.4 KiB
Groff
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.TH "EXCITED_STATES" "1" "Mar 07, 2019" "2.0" "Quantum Package"
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.SH NAME
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excited_states \- | Quantum Package >
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..
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.sp
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It is possible to run excited states calculations with the quantum
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package. To do this, set \fBdeterminants n_states\fP to the number
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of requested states. The selection criterion will be the maximum of the
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selection criteria for each state. If the Davidson diagonalization has
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difficulties to converge, increase the \fBdavidson n_states_diag\fP
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value.
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.sp
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When computing multiple states, it is good to have the
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\fBdeterminants s2_eig\fP flag \fBtrue\fP\&. This will force the Davidson
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algorithm to choose only vectors with a value of \ewidehat{S^2} equal to
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\fBdeterminants expected_s2\fP\&. Otherwise, different spin states
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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,
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excited states of different symmetries may enter in the calculation.
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Note that it is possible to make state\-average calculation of states
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with different symmetries 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
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to run a preliminary multi\-state CIS calculation using the CIS
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program, and then running the selected FCI restarting from the CIS
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states, setting \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
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all states have MOs of comparable quality. This allows for a faster
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convergence 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
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\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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2019, A. Scemama, E. Giner
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