Comparison of vertical and adiabatic harmonic approaches for the calculation of the vibrational structure of electronic spectra Francisco Avila and Fabrizio Santoro, a CNR--Consiglio Nazionale delle Ricerche, Istituto di Chimica dei Composti OrganoMetallici(ICCOM-CNR), UOS di Pisa, Area della Ricerca, via G. Moruzzi 1, I-56124 Pisa, Italy E-mail: fabrizio.santoro@iccom.cnr.it; We focus on effective models for the simulation of the vibrational structure associated to electronic spectra (VSaES) in large semi-rigid molecules with negligible nonadiabatic couplings. Any description of such a VSaES requires the determination of the potential energy surfaces (PES) of the electronic states involved in the transition. For large systems (dozens of atoms) an exhaustive exploration of the PESs on a grid of points is out of reach, and harmonic expansions of the PES around topical structures often represent the only viable route. In this context, two possible approaches can be adopted, namely the expansion of the final state PES around its own equilibrium geometry (Adiabatic) or around the initial state one (Vertical). Moreover, even within Harmonic approximation each of the two approaches gives rise to a hierarchy of models of different accuracy, depending on whether no constrain is imposed on the final state PES, apart from being harmonic (AH, Adiabatic Hessian or VH, Vertical Hessian), or the normal modes of the initial and final state are assumed to be the same but with possibly different frequencies (ASF, Adiabatic Shift and Frequencies or VGF, Vertical Gradient and Frequencies), or finally the two PES are assumed to be identical apart from a displacement of the minimum (AS, Adiabatic Shift or VG, Vertical Gradient). When it is necessary to go beyond the Franck-Condon (FC) approximation, including the Herzberg-Teller (HT) linear variation of the transition dipole as a function of the nuclear coordinates, other two different options are possible: namely, performing the expansion around the equilibrium geometry of the initial or final state. All these different models have been implemented in a version of our code FCclasses [1] that computes VSaES on the ground of effective pre-screening techniques to preselect only the relevant transitions in the dense manifold of possible final states [2]. The relative performance of these models on a number of prototypical dyes at low and room temperature will be discussed. [1]Santoro. F.; FCclasses a Fortran 77 code, 2008 http://village.pi.iccom.cnr.it [2] (a) Santoro, F.; Improta, R.; Lami, A.; Bloino, J.; Barone, V. J. Chem. Phys. 2007, 126, 084509, (b) Santoro, F.; Improta, R.; Lami, A.; Barone, V. J. Chem. Phys. 2007, 126, 184102. (c) Santoro, F.; Improta, R.; Lami, A.; Bloino, J.; Barone, V. J. Chem. Phys. 2008, 128, 224311. (d) Bloino, J.; Biczysko, M.; Santoro, F.; Barone, V., J. Chem. Theory and Comp. 2010, 1256. .
Comparison of vertical and adiabatic harmonic approaches for the Calculation of the vibrational structure of electronic spectra
F Santoro
2012
Abstract
Comparison of vertical and adiabatic harmonic approaches for the calculation of the vibrational structure of electronic spectra Francisco Avila and Fabrizio Santoro, a CNR--Consiglio Nazionale delle Ricerche, Istituto di Chimica dei Composti OrganoMetallici(ICCOM-CNR), UOS di Pisa, Area della Ricerca, via G. Moruzzi 1, I-56124 Pisa, Italy E-mail: fabrizio.santoro@iccom.cnr.it; We focus on effective models for the simulation of the vibrational structure associated to electronic spectra (VSaES) in large semi-rigid molecules with negligible nonadiabatic couplings. Any description of such a VSaES requires the determination of the potential energy surfaces (PES) of the electronic states involved in the transition. For large systems (dozens of atoms) an exhaustive exploration of the PESs on a grid of points is out of reach, and harmonic expansions of the PES around topical structures often represent the only viable route. In this context, two possible approaches can be adopted, namely the expansion of the final state PES around its own equilibrium geometry (Adiabatic) or around the initial state one (Vertical). Moreover, even within Harmonic approximation each of the two approaches gives rise to a hierarchy of models of different accuracy, depending on whether no constrain is imposed on the final state PES, apart from being harmonic (AH, Adiabatic Hessian or VH, Vertical Hessian), or the normal modes of the initial and final state are assumed to be the same but with possibly different frequencies (ASF, Adiabatic Shift and Frequencies or VGF, Vertical Gradient and Frequencies), or finally the two PES are assumed to be identical apart from a displacement of the minimum (AS, Adiabatic Shift or VG, Vertical Gradient). When it is necessary to go beyond the Franck-Condon (FC) approximation, including the Herzberg-Teller (HT) linear variation of the transition dipole as a function of the nuclear coordinates, other two different options are possible: namely, performing the expansion around the equilibrium geometry of the initial or final state. All these different models have been implemented in a version of our code FCclasses [1] that computes VSaES on the ground of effective pre-screening techniques to preselect only the relevant transitions in the dense manifold of possible final states [2]. The relative performance of these models on a number of prototypical dyes at low and room temperature will be discussed. [1]Santoro. F.; FCclasses a Fortran 77 code, 2008 http://village.pi.iccom.cnr.it [2] (a) Santoro, F.; Improta, R.; Lami, A.; Bloino, J.; Barone, V. J. Chem. Phys. 2007, 126, 084509, (b) Santoro, F.; Improta, R.; Lami, A.; Barone, V. J. Chem. Phys. 2007, 126, 184102. (c) Santoro, F.; Improta, R.; Lami, A.; Bloino, J.; Barone, V. J. Chem. Phys. 2008, 128, 224311. (d) Bloino, J.; Biczysko, M.; Santoro, F.; Barone, V., J. Chem. Theory and Comp. 2010, 1256. .I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
