Assessment of local coupled cluster methods for excited states of BODIPY/Aza‐BODIPY families

Abstract

It was previously reported that Laplace transformed local CC2 (LCC2*) provided the best agreement (MAE = 0.145 eV) when comparing vertical excitation energies to experimental λ max for a benchmark set of 17 BODIPY/Aza-BODIPY molecules. However, these energies did not agree with values obtained from canonical CC2. Here we report LCC2* computations of vertical excitation energies on the same benchmark set of molecules using a newly implemented treatment of the ground state. Comparison with resolution-of-identity approximate coupled cluster to second-order (RI-CC2) results demonstrate that the new LCC2* results agree quantitatively. Furthermore, these values can easily be corrected empirically to also provide excellent agreement with the experiment. We show that the local algebraic diagrammatic construction to second-order (LADC(2)) method exhibits the same differences between implementations as seen for LCC2. The source of the difference is traced to an improved treatment of the ground state in the local methods, which decreases agreement with the experiment (as attributed to a fortuitous cancellation of errors) but significantly improves agreement with RI-CC2. While the absolute vertical excitation energies now show larger deviations, there remains a strong linear correlation between the LCC2* results and the experiment. For the 17 BODIPY/Aza-BODIPY molecules vertical excitation energies are determined using DLPNO-STEOM-CCSD and shown to have excellent agreement with experimental λ max (MAE = 0.145 eV), which is the best of all the single-reference methods. The vertical excitation energies are determined using LCC2*, empirically corrected LCC2*, and RI-CC2 for a series of eight large BODIPYs and Aza-BODIPYs.

Accurate predictions of the electronic excited states of BODIPY based dye sensitizers using spin-component-scaled double-hybrid functionals: a TD-DFT benchmark study

“…55,70 Considering the average large size of dye sensitizers in general and the large size of the dyes investigated in this study, we have decided to adopt the vertical excitation regime. 46,55,66,70 Moreover, the practice of frequent calculations of large dyes in order to evaluate their potential use as light harvesting systems should be easy and straightforward. Thus it would be necessary to be able to calculate the optical properties of moderate to large size molecules using a simple protocol such as that of the vertical excitation energies, and not by using the complicated many-step protocol of nding E 0-0 values.…”

“…[46][47][48][49][50][51] Typically, push-pull dyes designed with the "electron donor-p linker-electron acceptor" (D-p-A) conventional architecture, and many other variations such as the D-A-p-A architecture, 52 are found to be efficient for photosensitized applications such as DSSCs. 14,53 Despite many theoretical and computational efforts, [54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70] the electronic molecular spectroscopy of BODIPYs is still not yet fully understood, and the accurate calculation of their excitedstates is still a challenge for both theoretical and computational chemists. In general, conventional time dependent (TD) DFT is the preferred method for electronic excited states calculations on large compounds, since it is efficient and reasonably accurate, with errors of transition energies in the range 0.1-0.3 eV for many simple organic chromophores.…”

“…Unfortunately, TD-DFT tends to highly overestimates the low-initio and TD-DFT methods, such as combined TD-DFT and SOS-CIS(D), [59][60][61] combined TD-DFT and Bethe-Salpeter formalism, 62 spin-ip TD-DFT approach, 63 and coupled-cluster methods. 55,[64][65][66][67][68] For instance, Brown and coworkers found that the mean absolute error (MAE) of the Laplace transformed local CC2 (LCC2*) and the DLPNO-STEOM-CCSD methods are around 0.1 eV. 55,66 It should be emphasized, however, that these two accurate coupled-cluster methods, cannot be applied for reasonably large molecules.…”

“…55,[64][65][66][67][68] For instance, Brown and coworkers found that the mean absolute error (MAE) of the Laplace transformed local CC2 (LCC2*) and the DLPNO-STEOM-CCSD methods are around 0.1 eV. 55,66 It should be emphasized, however, that these two accurate coupled-cluster methods, cannot be applied for reasonably large molecules.…”

“…70 The average of errors found in that benchmark study using TD DH functionals fall in the range of errors of the more expensive coupled-cluster methods. 55,66 In this work, we have decided to extend the benchmark of double hybrid functionals, on larger dyes that are designed on push-pull architectures and having electronic transitions that are characterized with signicant long range charge transfer. The double hybrid functionals are not frequently used for the computational description of the optical properties of BODIPY and other dye sensitizers.…”