restricted number of active electronic excited states in the dynamical process. The
lack of coherence and phase of the nuclei and the total time per trajectory are the
limiting factors of semi-classical trajectory surface hopping. The advantages are the
inclusion of all nuclear degrees of freedom, the use of on-the-fly calculated potentials, and the ease of improving accuracy by including more trajectories.
The applicability of the full quantum approach is limited by the nuclear dimensionality and requires very robust electronic structure methods for excited states
[70, 110]. The drawbacks of wavepacket dynamics are the complexity of setting up
an appropriate effective Hamiltonian, the use of approximate fitted potentials, and
the choice of selected vibrational modes.
The pioneering dynamical simulations performed on transition metal complexes
are far from being routine and need specific developments to be applicable to a wide
range of systems and ultra-fast phenomena circumscribed by spin-vibronic coupling [111]. Recent applications to first-, second-, and third-row transition metal
complexes based on various approaches are developed in section 5 dedicated to
ultra-fast ISC processes.
3 Absorption Spectroscopy
The purpose of the next sections devoted to the absorption spectroscopy of thirdrow transition metal complexes is to illustrate by recent examples the importance of
SOC in the computation of TD-DFT vertical electronic spectra using ZORA
approach. Whenever possible, the SOC-TD-DFT approach is compared to the
SOC-CASSCF/MS-CASPT2 method based on RASSI. In these examples the
electronic SOC effect is treated independent of any nuclear relaxation that could
influence its contribution to the absorption spectra.
3.1 Electronic Spectroscopy of Ir(III) Complexes
In this application the absorption spectra of [Ir (ppy) 3 ] 1 and [Ir (ppy) 2 (CO)Cl)] 2
(ppy ¼ tris(2-phenylpyridine) (Scheme 1) have been calculated by means of
TD-DFT methods based on optimized structures in vacuum and including spinorbit coupling [80].
Both TD-DFT/B3LYP and TD-DFT/PW91 “spin-free” absorption spectra have
been computed. The TD-DFT/B3LYP results shift the theoretical spectrum of
[Ir (ppy) 3 ] 1 to the blue, as compared to the PW91 results, by 0.75 eV, with a
first transition calculated at 25,080 cm
À1 of significant oscillator strength
( f ¼ 0.023). Moreover, this overestimated transition is characterized by an important unrealistic ligand-to-ligand-charge-transfer (LLCT) character which is only
minor in the TD-DFT/PW91.
Absorption Spectroscopy, Emissive Properties, and Ultrafast Intersystem. . .
385
lack of coherence and phase of the nuclei and the total time per trajectory are the
limiting factors of semi-classical trajectory surface hopping. The advantages are the
inclusion of all nuclear degrees of freedom, the use of on-the-fly calculated potentials, and the ease of improving accuracy by including more trajectories.
The applicability of the full quantum approach is limited by the nuclear dimensionality and requires very robust electronic structure methods for excited states
[70, 110]. The drawbacks of wavepacket dynamics are the complexity of setting up
an appropriate effective Hamiltonian, the use of approximate fitted potentials, and
the choice of selected vibrational modes.
The pioneering dynamical simulations performed on transition metal complexes
are far from being routine and need specific developments to be applicable to a wide
range of systems and ultra-fast phenomena circumscribed by spin-vibronic coupling [111]. Recent applications to first-, second-, and third-row transition metal
complexes based on various approaches are developed in section 5 dedicated to
ultra-fast ISC processes.
3 Absorption Spectroscopy
The purpose of the next sections devoted to the absorption spectroscopy of thirdrow transition metal complexes is to illustrate by recent examples the importance of
SOC in the computation of TD-DFT vertical electronic spectra using ZORA
approach. Whenever possible, the SOC-TD-DFT approach is compared to the
SOC-CASSCF/MS-CASPT2 method based on RASSI. In these examples the
electronic SOC effect is treated independent of any nuclear relaxation that could
influence its contribution to the absorption spectra.
3.1 Electronic Spectroscopy of Ir(III) Complexes
In this application the absorption spectra of [Ir (ppy) 3 ] 1 and [Ir (ppy) 2 (CO)Cl)] 2
(ppy ¼ tris(2-phenylpyridine) (Scheme 1) have been calculated by means of
TD-DFT methods based on optimized structures in vacuum and including spinorbit coupling [80].
Both TD-DFT/B3LYP and TD-DFT/PW91 “spin-free” absorption spectra have
been computed. The TD-DFT/B3LYP results shift the theoretical spectrum of
[Ir (ppy) 3 ] 1 to the blue, as compared to the PW91 results, by 0.75 eV, with a
first transition calculated at 25,080 cm
À1 of significant oscillator strength
( f ¼ 0.023). Moreover, this overestimated transition is characterized by an important unrealistic ligand-to-ligand-charge-transfer (LLCT) character which is only
minor in the TD-DFT/PW91.
Absorption Spectroscopy, Emissive Properties, and Ultrafast Intersystem. . .
385