Resonance Raman Input options

A number of options are available for the VIBRON module, most of which are for special applications. All the options mentioned below have to appear in the VIBRON block. The VIBRON module always requires an EXCITATION input block, in which the total number of excited states to be calculated must be specified.

VIBRON
 NMTAPE filename
 RESRAMAN
 {DISPTYPE disptype}
 {STPSIZE stpsize}
 {ONLYSYM}
 {NOTONLYSYM}
 {DOMODES list}
 {DONTMODES list}
 {DSCHEME dscheme}
 {EUTHRES euthres}
 {ELTHRES elthres}
 {SELSTATE list}
 {SAVERAWDAT}
 {USERAWDAT}
END

The most important ones in connection with RR calculations are:

NMTAPE filename

NMTAPE is the only obligatory keyword for the VIBRON module. It specifies the name of a TAPE21 file from a previous frequency calculation. This TAPE21 file is needed to read the normal modes w.r.t. which the derivatives are computed. I.e., a separate frequency calculation must be carried out first.

RESRAMAN

The second subkeyword RESRAMAN invokes the resonance Raman calculation.

DISPTYPE disptype

Select type of displacement steps; possible values are:
- MASSWE: steps in terms of mass-weighted normal mode vectors [default]
- CARTES: steps in terms of cartesian normal mode vectors
- REDUCE: steps in terms of reduced normal modes
- ENERGY: steps in terms of expected energy change (according to harmonic approximation)
- ZPELEV: like energy, but energy is expressed in ZPE units

STPSIZE stpsize

Sets the step size for the numerical differentiation in the default unit for the given DISPTYPE

ONLYSYM

Calculate derivatives only for totally symmetric modes (this is useful since this RR estimate only holds for Franck-Condon type Raman scattering, which is zero for non-symmetric modes). This option is ON per default in RR calculations, it can be switched off with the key NOTONLYSYM.

DOMODES list

Calculate derivatives only for the normal modes with numbers mentioned in list.

DONTMODES list

Calculate derivatives for all normal modes except the ones with numbers mentioned in list.

DSCHEME dscheme

The type of differentiation to be used can be set. Three different values for dscheme are available:

ELCHAR

A simple diabatic picture in which adiabatic states are mapped to the adiabatic states for the references structure based on a maximum transition density overlap criterion [default].

EIGVEC

A diabatic picture in which a diabatization is carried out as explained in Ref. [203]. I.e. the energies used here are the diagonal elements of the potential energy matrix for the nuclear Schrödinger Equation.

ADIABS

The adiabatic picture; can only be used if the symmetry of the excited states is supplied from a separate calculation, since the VIBRON module cannot check which states are allowed to cross as no symmetry is used in the excitation calculations. Consult the ADF-VIBRON manual [204] for information.

ELTHRESH elthresh
EUTHRESH euthresh

For advanced users it is possible to set an energy window within the range of states calculated, and only the states within this energy window will be taken into account in the evaluation.
- elthresh: lower bound in eV, default 0 eV.
- euthresh: upper bound in eV, default 1.0E10 eV.

SELSTATE list

For advanced users it is furthermore possible to pick out certain states from the energy window, and only perform the mapping (and diabatization, if requested) and differentiation for them. Here list includes the number (in ascending excitation energy) of the excited state at the reference (equilibrium) structure.

SAVERAWDAT

All raw data are saved to TAPE21, which might be an enormous amount of data. The selected states and the energy window settings can then be adjusted in a restart (with the usual restart key) and the inclusion of the subkey USERAWDATA after all single-point calculations are done.

USERAWDAT

All raw data are read from a previous calculation. The selected states and the energy window settings can now be adjusted. You need to invoke the usual restart key. Such a restart does not invoke any new SCF and will, therefore, typically only take a couple of seconds or minutes. If SAVERAWDAT is not specified in the previuous calculation, restarts are still possible, but the energy window cannot be adjusted differently, and no new state selection can be performed.