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--- franck-condon_calculations [2025/02/05 13:02] – rauhut
+++ franck-condon_calculations [2025/02/07 13:01] (current) – rauhut
@@ Line 5: / Line 5: @@
 ''FCON'',//options// [fcon]
-The ''FCON'' program allows for the calculation of Franck-Condon factors based on potential energy surfaces obtained from the ''SURF'' and ''XSURF'' programs and vibrational wavefunctions as provided by the ''VSCF'' or ''VCI'' programs. Duschinsky effects may or may not be included. These can either be applied to the vibrational wavefunction (of the vibrational ground state) or the potential by using the ''PESTRANS'' program. The latter possibility is the recommended one as it is significantly faster. The ''FCON'' program including Duschinsky rotations can only be used with analytical representations of the potential energy surfaces. A prescreening of the Franck-Condon factors without Duschinsky effects at the ''VSCF'' level is used to reduce the computational effort for correlated levels, e.g. ''VCI''. Note that, Franck-Condon factors at the uncorrelated ''VSCF'' level including Duschinsky effects are usually of fairly poor quality. As the calculation of Franck-Condon factors often involves very high quantum numbers for the vibrational states of the final electronic state, very high excitation levels must be enabled in the ''VCI'' calculations, i.e. see keyword ''LEVEX''. As a consequence, the ''SCALE'' parameter in ''SURF'' calculations needs to be modified in most applications. For details see:\\
+The ''FCON'' program allows for the calculation of Franck-Condon factors based on potential energy surfaces obtained from the ''XSURF'' program and vibrational wavefunctions as provided by the ''VSCF'' or ''VCI'' programs. Duschinsky effects may or may not be included. These can either be applied to the vibrational wavefunction (of the vibrational ground state) or the potential by using the ''PESTRANS'' program. The latter possibility is the recommended one as it is significantly faster. The ''FCON'' program including Duschinsky rotations can only be used with analytical representations of the potential energy surfaces. A prescreening of the Franck-Condon factors without Duschinsky effects at the ''VSCF'' level is used to reduce the computational effort for correlated levels, e.g. ''VCI''. Note that, Franck-Condon factors at the uncorrelated ''VSCF'' level including Duschinsky effects are usually of fairly poor quality. As the calculation of Franck-Condon factors often involves very high quantum numbers for the vibrational states of the final electronic state, very high excitation levels must be enabled in the ''VCI'' calculations, i.e. see keyword ''LEVEX''. For details see:\\
 P. Meier, G. Rauhut, //Comparison of methods for calculating Franck-Condon factors beyond the harmonic approximation: how important are Duschinsky rotations?//, [[https://dx.doi.org/10.1080/00268976.2015.1074740|Mol. Phys.]] **113**, 3859 (2015).\\
 G. Rauhut, //Anharmonic Franck-Condon factors for the  $\tilde{\mbox{X}}\,{}^2$ B ${}_1 \longleftarrow \tilde{\mbox{X}}\,{}^1$ A ${}_1$  photoionization of ketene//, J. Phys. Chem. A **119**, (2015) 10264.\\
@@ Line 28: / Line 28: @@
   * **''WF''=//type//** Defines the type of the wavefunction. ''WF=VSCF'' specifies state-specific ''VSCF'' wavefunctions for both levels, while ''WF=VCI'' denotes state-specific ''VCI'' wavefunctions. Alternatively, one may use ''WF=VSCFG'' for ground-state based VSCF wavefunctions and ''WF=VCIG'' for ground-state based VCI wavefunctions. The default is ''WF=VCI''.
-Some of the keywords as described for the ''VCI'' program are also valid for the ''FCON'' program, i.e. ''%%CITYPE, LEVEX, CIMAX, DIPOLE, NDIM, NBAS, NGRID, BASIS%%'' and ''INFO''.
+Some of the keywords as described for the ''VCI'' program are also valid for the ''FCON'' program, i.e. ''%%CITYPE, LEVEX, CIMAX, NDIM, NBAS, BASIS%%'' and ''INFO''.
 ==== Information Handling ====
@@ Line 323: / Line 323: @@
 The following example shows a general program flow involving the ''EVSPEC'' calculations.
+<code>
+memory,40,m
+basis=vdz
+geometry={
+H   ,,     2.3971901752  ,    -2.3962403391   ,    0.0000000000
+S   ,,    -0.0873406755  ,    -1.8178592700   ,    0.0000000000
+S   ,,     0.0117763411  ,     1.8933936636   ,    0.0000000000
+}
+basis=vdz
+hf
+{xsurf                                            ! reads the PES of the initial electronic
+ disk,where=home,extern='initial.pot'}            ! state from 'initial.pot'
+poly                                              ! Transform  the initial PES to the
+vscf,pot=poly                                     ! representation in terms of the normal
+vci,pot=poly                                      ! coordinates of the final PES
+                                                  ! (stored in 'final.pot'), and fit it
+{pestrans,info=1                                  ! with polynomial functions.
+ disk,where=home,auto=1,extern='final.pot'}       ! All results for the initial surface
+                                                  ! are stored with the reference number
+{poly                                             ! given by the keyword auto=1.
+ disk,auto=1}
+{vscf,pot=poly                                    ! Run VSCF calculations for initial states.
+ disk,auto=1}
+{vci,pot=poly,export='EVSPEC'                     ! Run VCI calculations for initial states.
+ disk,auto=1}
+{xsurf                                            ! Reads the PES of the final electronic
+ disk,where=home,auto=2,extern='final.pot'}       ! state from 'final.pot'.
+{poly                                             ! Provides the polynomial representation
+ disk,auto=2}                                     ! of the final PES.
+{vscf,pot=poly                                    ! Run VSCF calculations for generating
+ disk,auto=2}                                     ! vibrational modals for the final PES.
+{evspec,method=rwf,start=1,final=2,info=1         ! Simple input for the RWF calculation
+graph, evsdump='hs2_rwf.gnu'}
+</code>
+<!--
 <code>
 memory,20,m
@@ Line 414: / Line 457: @@
 </code>
+-->