2 Advanced Electronic Structure Theory for High-Accuracy …
39
the biradical character is slightly more weighted toward Open 1 relative to Open 2,
while the quinoidal character is less, as summarized in Fig. 2.6. The S2 state of the
open form appears to closely correspond to the electronic character of the S0 state
of the closed form, which was calculated to be a closed-shell state. The absorption
of visible light for the open form is mainly characterized by a transition from S0 to
S2 with its largest oscillator strength.
2.5 Conclusion
We have described an overview of our development of the DMRG-XMS-CASPT2
method (Ref. [29]) tailored toward highly reliable excited-state calculations of photochemical reactions including photochromic systems. The applications of this method
to photochormic systems, diarylethene derivatives and pentaarylbiimidazole, have
been discussed to stress the importance of multireference and multi-state treatments for achieving high accuracy in framework of quantum chemical calculations.
Recently, in Ref. [25], this approach was further extended by combining the solvation theory, RISM, to account for solvation effects in excited states. This technique is
important for studying bioimaging probes with photo-activity because these molecular systems are in many cases handled in solution. Earlier studies showed that they
cannot be described with conventional methods such as PCM-TD-DFT, yielding
results far from experimental data. Our DMRG-CASPT2 using the RISM solvation theory was shown to be powerful for calculating the photochemical properties
of near-infrared bioimaging molecules in solution with higher-accuracy prediction.
We hope that the establishment of these efficient computational approaches should
pave the way toward deeper and further detailed understanding of the mechanism of
photochromic reactions.
Acknowledgements T. Yanai greatly thanks Professors H. Miyasaka, J. Abe, Y. Shigeta,
Y. Kobayashi, A. Sakamoto, H. Sotome, and K. Mutoh for their collaboration. The present work
was supported by JSPS KAKENHI Grant Number 17H05274, Grant-in-Aid for Scientific Research
on Innovative Areas “Photosynergetics”.
References
1. Andersson K, Malmqvist PÅ, Roos BO, Sadlej AJ, Wolinski K (1990) Second-order perturbation theory with a casscf reference function. J Phys Chem 94:5483–5488
2. Andersson K, Malmqvist PÅ, Roos BO (1992) Second-order perturbation theory with a complete active space self-consistent field reference function. J Chem Phys 96:1218–1226
3. Angeli C, Borini S, Cestari M, Cimiraglia R (2004) A quasidegenerate formulation of the second
order n-electron valence state perturbation theory approach. J Chem Phys 121(9):4043–4049
4. Bloch C (1958) Sur la théorie des perturbations des états liés. Nuc Phys 6:329–347
5. block verion 1.1: an implementation of the density matrix renormalization group (DMRG)
algorithm for quantum chemistry. https://github.com/sanshar/Block
39
the biradical character is slightly more weighted toward Open 1 relative to Open 2,
while the quinoidal character is less, as summarized in Fig. 2.6. The S2 state of the
open form appears to closely correspond to the electronic character of the S0 state
of the closed form, which was calculated to be a closed-shell state. The absorption
of visible light for the open form is mainly characterized by a transition from S0 to
S2 with its largest oscillator strength.
2.5 Conclusion
We have described an overview of our development of the DMRG-XMS-CASPT2
method (Ref. [29]) tailored toward highly reliable excited-state calculations of photochemical reactions including photochromic systems. The applications of this method
to photochormic systems, diarylethene derivatives and pentaarylbiimidazole, have
been discussed to stress the importance of multireference and multi-state treatments for achieving high accuracy in framework of quantum chemical calculations.
Recently, in Ref. [25], this approach was further extended by combining the solvation theory, RISM, to account for solvation effects in excited states. This technique is
important for studying bioimaging probes with photo-activity because these molecular systems are in many cases handled in solution. Earlier studies showed that they
cannot be described with conventional methods such as PCM-TD-DFT, yielding
results far from experimental data. Our DMRG-CASPT2 using the RISM solvation theory was shown to be powerful for calculating the photochemical properties
of near-infrared bioimaging molecules in solution with higher-accuracy prediction.
We hope that the establishment of these efficient computational approaches should
pave the way toward deeper and further detailed understanding of the mechanism of
photochromic reactions.
Acknowledgements T. Yanai greatly thanks Professors H. Miyasaka, J. Abe, Y. Shigeta,
Y. Kobayashi, A. Sakamoto, H. Sotome, and K. Mutoh for their collaboration. The present work
was supported by JSPS KAKENHI Grant Number 17H05274, Grant-in-Aid for Scientific Research
on Innovative Areas “Photosynergetics”.
References
1. Andersson K, Malmqvist PÅ, Roos BO, Sadlej AJ, Wolinski K (1990) Second-order perturbation theory with a casscf reference function. J Phys Chem 94:5483–5488
2. Andersson K, Malmqvist PÅ, Roos BO (1992) Second-order perturbation theory with a complete active space self-consistent field reference function. J Chem Phys 96:1218–1226
3. Angeli C, Borini S, Cestari M, Cimiraglia R (2004) A quasidegenerate formulation of the second
order n-electron valence state perturbation theory approach. J Chem Phys 121(9):4043–4049
4. Bloch C (1958) Sur la théorie des perturbations des états liés. Nuc Phys 6:329–347
5. block verion 1.1: an implementation of the density matrix renormalization group (DMRG)
algorithm for quantum chemistry. https://github.com/sanshar/Block